Correction Appended: May 9, 2013

I am about to do what old people have done throughout history: call those younger than me lazy, entitled, selfish and shallow. But I have studies! I have statistics! I have quotes from respected academics! Unlike my parents, my grandparents and my great-grandparents, I have proof.

Here's the cold, hard data: The incidence of narcissistic personality disorder is nearly three times as high for people in their 20s as for the generation that's now 65 or older, according to the National Institutes of Health; 58% more college students scored higher on a narcissism scale in 2009 than in 1982. Millennials got so many participation trophies growing up that a recent study showed that 40% believe they should be promoted every two years, regardless of performance. They are fame-obsessed: three times as many middle school girls want to grow up to be a personal assistant to a famous person as want to be a Senator, according to a 2007 survey; four times as many would pick the assistant job over CEO of a major corporation. They're so convinced of their own greatness that the National Study of Youth and Religion found the guiding morality of 60% of millennials in any situation is that they'll just be able to feel what's right. Their development is stunted: more people ages 18 to 29 live with their parents than with a spouse, according to the 2012 Clark University Poll of Emerging Adults. And they are lazy. In 1992, the nonprofit Families and Work Institute reported that 80% of people under 23 wanted to one day have a job with greater responsibility; 10 years later, only 60% did.

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Millennials consist, depending on whom you ask, of people born from 1980 to 2000. To put it more simply for them, since they grew up not having to do a lot of math in their heads, thanks to computers, the group is made up mostly of teens and 20-somethings. At 80 million strong, they are the biggest age grouping in American history. Each country's millennials are different, but because of globalization, social media, the exporting of Western culture and the speed of change, millennials worldwide are more similar to one another than to older generations within their nations. Even in China, where family history is more important than any individual, the Internet, urbanization and the one-child policy have created a generation as overconfident and self-involved as the Western one. And these aren't just rich-kid problems: poor millennials have even higher rates of narcissism, materialism and technology addiction in their ghetto-fabulous lives.

They are the most threatening and exciting generation since the baby boomers brought about social revolution, not because they're trying to take over the Establishment but because they're growing up without one. The Industrial Revolution made individuals far more powerful--they could move to a city, start a business, read and form organizations. The information revolution has further empowered individuals by handing them the technology to compete against huge organizations: hackers vs. corporations, bloggers vs. newspapers, terrorists vs. nation-states, YouTube directors vs. studios, app-makers vs. entire industries. Millennials don't need us. That's why we're scared of them.

In the U.S., millennials are the children of baby boomers, who are also known as the Me Generation, who then produced the Me Me Me Generation, whose selfishness technology has only exacerbated. Whereas in the 1950s families displayed a wedding photo, a school photo and maybe a military photo in their homes, the average middle-class American family today walks amid 85 pictures of themselves and their pets. Millennials have come of age in the era of the quantified self, recording their daily steps on FitBit, their whereabouts every hour of every day on PlaceMe and their genetic data on 23 and Me. They have less civic engagement and lower political participation than any previous group. This is a generation that would have made Walt Whitman wonder if maybe they should try singing a song of someone else.

They got this way partly because, in the 1970s, people wanted to improve kids' chances of success by instilling self-esteem. It turns out that self-esteem is great for getting a job or hooking up at a bar but not so great for keeping a job or a relationship. "It was an honest mistake," says Roy Baumeister, a psychology professor at Florida State University and the editor of Self-Esteem: The Puzzle of Low Self-Regard. "The early findings showed that, indeed, kids with high self-esteem did better in school and were less likely to be in various kinds of trouble. It's just that we've learned later that self-esteem is a result, not a cause." The problem is that when people try to boost self-esteem, they accidentally boost narcissism instead. "Just tell your kids you love them. It's a better message," says Jean Twenge, a psychology professor at San Diego State University, who wrote Generation Me and The Narcissism Epidemic. "When they're little it seems cute to tell them they're special or a princess or a rock star or whatever their T-shirt says. When they're 14 it's no longer cute." All that self-esteem leads them to be disappointed when the world refuses to affirm how great they know they are. "This generation has the highest likelihood of having unmet expectations with respect to their careers and the lowest levels of satisfaction with their careers at the stage that they're at," says Sean Lyons, co-editor of Managing the New Workforce: International Perspectives on the Millennial Generation. "It is sort of a crisis of unmet expectations."

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What millennials are most famous for besides narcissism is its effect: entitlement. If you want to sell seminars to middle managers, make them about how to deal with young employees who e-mail the CEO directly and beg off projects they find boring. English teacher David McCullough Jr.'s address last year to Wellesley High School's graduating class, a 12-minute reality check titled "You Are Not Special," has nearly 2 million hits on YouTube. "Climb the mountain so you can see the world, not so the world can see you," McCullough told the graduates. He says nearly all the response to the video has been positive, especially from millennials themselves; the video has 57 likes for every dislike.

Though they're cocky about their place in the world, millennials are also stunted, having prolonged a life stage between teenager and adult that this magazine once called twixters and will now use once again in an attempt to get that term to catch on. The idea of the teenager started in the 1920s; in 1910, only a tiny percentage of kids went to high school, so most people's social interactions were with adults in their family or in the workplace. Now that cell phones allow kids to socialize at every hour--they send and receive an average of 88 texts a day, according to Pew--they're living under the constant influence of their friends. "Peer pressure is anti-intellectual. It is anti-historical. It is anti-eloquence," says Mark Bauerlein, an English professor at Emory, who wrote The Dumbest Generation: How the Digital Age Stupefies Young Americans and Jeopardizes Our Future (Or, Don't Trust Anyone Under 30). "Never before in history have people been able to grow up and reach age 23 so dominated by peers. To develop intellectually you've got to relate to older people, older things: 17-year-olds never grow up if they're just hanging around other 17-year-olds." Of all the objections to Obamacare, not a lot of people argued against parents' need to cover their kids' health insurance until they're 26.

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Millennials are interacting all day but almost entirely through a screen. You've seen them at bars, sitting next to one another and texting. They might look calm, but they're deeply anxious about missing out on something better. Seventy percent of them check their phones every hour, and many experience phantom pocket-vibration syndrome. "They're doing a behavior to reduce their anxiety," says Larry Rosen, a psychology professor at California State University at Dominguez Hills and the author of iDisorder. That constant search for a hit of dopamine ("Someone liked my status update!") reduces creativity. From 1966, when the Torrance Tests of Creative Thinking were first administered, through the mid-1980s, creativity scores in children increased. Then they dropped, falling sharply in 1998. Scores on tests of empathy similarly fell sharply, starting in 2000, likely because of both a lack of face-to-face time and higher degrees of narcissism. Not only do millennials lack the kind of empathy that allows them to feel concerned for others, but they also have trouble even intellectually understanding others' points of view.

What they do understand is how to turn themselves into brands, with "friend" and "follower" tallies that serve as sales figures. As with most sales, positivity and confidence work best. "People are inflating themselves like balloons on Facebook," says W. Keith Campbell, a psychology professor at the University of Georgia, who has written three books about generational increases in narcissism (including When You Love a Man Who Loves Himself). When everyone is telling you about their vacations, parties and promotions, you start to embellish your own life to keep up. If you do this well enough on Instagram, YouTube and Twitter, you can become a microcelebrity.

Millennials grew up watching reality-TV shows, most of which are basically documentaries about narcissists. Now they have trained themselves to be reality-TV-ready. "Most people never define who they are as a personality type until their 30s. So for people to be defining who they are at the age of 14 is almost a huge evolutionary jump," says casting director Doron Ofir, who auditioned participants for Jersey Shore, Millionaire Matchmaker, A Shot at Love and RuPaul's Drag Race, among other shows. "Do you follow me on Twitter?" he asks at the end of the interview. "Oh, you should. I'm fun. I hope that one day they provide an Emmy for casting of reality shows--because, you know, I'd assume I'm a shoo-in. I would like that gold statue. And then I will take a photo of it, and then I will Instagram it." Ofir is 41, but he has clearly spent a lot of time around millennials.

I have gone just about as far as I can in an article without talking about myself. So first, yes, I'm aware that I started this piece--in which I complain about millennials' narcissism--with the word I. I know that this magazine, which for decades did not print bylines, started putting authors' names on the cover regularly in 2004 and that one of the first names was mine. As I mocked reality shows in the previous paragraph, I kept thinking about the fact that I got to the final round for 1995's Real World: London. I know my number of Twitter followers far better than the tally on my car's odometer; although Facebook has a strictly enforced limit of 5,000 friends, I somehow have 5,079. It was impossible not to remember, the whole time I was accusing millennials of being lazy, that I was supposed to finish this article nearly a year ago.

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I moved home for the first six months after college. When I got hired at Time, my co-workers hated me for cozying up to the editor of the magazine. I talk to one of my parents every other day and depend on my dad for financial advice. It's highly possible that I'm a particularly lame 41-year-old, but still, none of these traits are new to millennials; they've been around at least since the Reformation, when Martin Luther told Christians they didn't need the church to talk to God, and became more pronounced at the end of the 18th century in the Romantic period, when artists stopped using their work to celebrate God and started using it to express themselves. In 1979, Christopher Lasch wrote in The Culture of Narcissism, "The media give substance to, and thus intensify, narcissistic dreams of fame and glory, encourage common people to identify themselves with the stars and to hate the 'herd,' and make it more and more difficult for them to accept the banality of everyday existence." I checked my e-mail three times during that sentence.

So while the entire first half of this article is absolutely true (I had data!), millennials' self-involvement is more a continuation of a trend than a revolutionary break from previous generations. They're not a new species; they've just mutated to adapt to their environment.

For example, millennials' perceived entitlement isn't a result of overprotection but an adaptation to a world of abundance. "For almost all of human history, almost everyone was a small-scale farmer. And then people were farmers and factory workers. Nobody gets very much fulfillment from either of those things," says Jeffrey Arnett, a psychology professor at Clark University, who invented the phrase emerging adulthood, which people foolishly use instead of the catchy twixters . Twixters put off life choices because they can choose from a huge array of career options, some of which, like jobs in social media, didn't exist 10 years ago. What idiot would try to work her way up at a company when she's going to have an average of seven jobs before age 26? Because of online dating, Facebook circles and the ability to connect with people internationally, they no longer have to marry someone from their high school class or even their home country. Because life expectancy is increasing so rapidly and technology allows women to get pregnant in their 40s, they're more free to postpone big decisions. The median age for an American woman's first marriage went from 20.6 in 1967 to 26.9 in 2011.

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And while all that choice might end in disappointment, it's a lottery worth playing. "I had one grandfather fight in the Pacific and one in the Atlantic theater. One became a pilot; one became a doctor. When you grow up during the Great Depression and fight off the Nazis, you want safety and stability," says Tucker Max, 37, who set an example for millennials when instead of using his Duke law degree to practice law, he took his blog rants about his drunken, lecherous adventures and turned them into a mega-best-selling book, I Hope They Serve Beer in Hell, that he got an independent publisher to print. "Everyone told you that everyone above you had to s--- on you before you got to s--- on people below you. And millennials didn't want to do that."

In fact, a lot of what counts as typical millennial behavior is how rich kids have always behaved. The Internet has democratized opportunity for many young people, giving them access and information that once belonged mostly to the wealthy. When I was growing up in the 1980s, I thought I would be a lawyer, since that was the best option I knew about for people who sucked at math in my middle-class suburb, but I saw a lot more options once I got to Stanford. "Previously if you wanted to be a writer but didn't know anyone who is in publishing, it was just, Well, I won't write. But now it's, Wait, I know someone who knows someone," says Jane Buckingham, who studies workplace changes as founder of Trendera, a consumer-insights firm. "I hear story after story of people high up in an organization saying, 'Well, this person just e-mailed me and asked me for an hour of my time, and for whatever reason I gave it to them.' So the great thing is that they do feel entitled to all of this, so they'll be more innovative and more willing to try new things and they'll do all this cool stuff."

Because millennials don't respect authority, they also don't resent it. That's why they're the first teens who aren't rebelling. They're not even sullen. "I grew up watching Peanuts, where you didn't even see the parents. They were that 'Wah-wah' voice. And MTV was always a parent-free zone," says MTV president Stephen Friedman, 43, who now includes parents in nearly all the channel's reality shows. "One of our research studies early on said that a lot of this audience outsources their superego to their parents. The most simple decision of should I do this or should I do that--our audience will check in with their parents." A 2012 Google Chrome ad shows a college student video-chatting all the details of her life to her dad. "I am very used to seeing things where the cliché is the parent doesn't understand. Most of my friends, their parents are on social and they're following them or sharing stuff with them," says Jessica Brillhart, a filmmaker at Google's Creative Lab, who worked on the commercial. It's hard to hate your parents when they also listen to rap and watch Jon Stewart.

In fact, many parents of millennials would proudly call their child-rearing style peer-enting. "I negotiate daily with my son who is 13. Maybe all that coddling has paid off in these parent-child relationships," says Jon Murray, who created The Real World and other reality shows, including Keeping Up With the Kardashians. He says that seeing regular people celebrated on TV gives millennials confidence: "They're going after what they want. It can be a little irritating that they want to be on the next rung so quickly. Maybe I'm partly responsible for it. I like this generation, so I have no issues with that."

Kim Kardashian, who represents to nonmillennials all that is wrong with her generation, readily admits that she has no particular talent. But she also knows why she appeals to her peers. "They like that I share a lot of myself and that I've always been honest about the way I live my life," she says. "They want relationships with businesses and celebrities. Gen X was kept at arm's length from businesses and celebrity." When you're no longer cowed by power, you are going to like what a friend tells you about far more than what an ad campaign does, even if that friend is a celebrity trying to make money and that friendship is just a reply to one tweet.

While every millennial might seem like an oversharing Kardashian, posting vacation photos on Facebook is actually less obnoxious than 1960s couples' trapping friends in their houses to watch their terrible vacation slide shows. "Can you imagine if the boomers had YouTube, how narcissistic they would've seemed?" asks Scott Hess, senior vice president of human intelligence for SparkSMG, whose TedX speech, "Millennials: Who They Are and Why We Hate Them," advised companies on marketing to youth. "Can you imagine how many frickin' Instagrams of people playing in the mud during Woodstock we would've seen? I think in many ways you're blaming millennials for the technology that happens to exist right now." Yes, they check their phones during class, but think about how long you can stand in line without looking at your phone. Now imagine being used to that technology your whole life and having to sit through algebra.

Companies are starting to adjust not just to millennials' habits but also to their atmospheric expectations. Nearly a quarter of DreamWorks' 2,200 employees are under 30, and the studio has a 96% retention rate. Dan Satterthwaite, who runs the studio's human-relations department and has been in the field for about 23 years, says Maslow's hierarchy of needs makes it clear that a company can't just provide money anymore but also has to deliver self-actualization. During work hours at DreamWorks, you can take classes in photography, sculpting, painting, cinematography and karate. When one employee explained that jujitsu is totally different from karate, Satterthwaite was shocked at his boldness, then added a jujitsu class.

Millennials are able to use their leverage to negotiate much better contracts with the traditional institutions they do still join. Although the armed forces had to lower the physical standards for recruits and make boot camp less intensive, Gary Stiteler, who has been an Army recruiter for about 15 years, is otherwise more impressed with millennials than any other group he's worked with. "The generation that we enlisted when I first started recruiting was sort of do, do, do. This generation is think, think about it before you do it," he says. "This generation is three to four steps ahead. They're coming in saying, 'I want to do this, then when I'm done with this, I want to do this.'"

Here's something even all the psychologists who fret over their narcissism studies agree about: millennials are nice. They have none of that David Letterman irony and Gen X ennui. "The positivism has surprised me. The Internet was always 50-50 positive and negative. And now it's 90-10," says Shane Smith, the 43-year-old CEO of Vice, which adjusted from being a Gen X company in print to a millennial company once it started posting videos online, which are viewed by a much younger audience. Millennials are more accepting of differences, not just among gays, women and minorities but in everyone. "There are many, many subcultures, and you can dip into them and search around. I prefer that to you're either supermainstream or a riot grrrl," says Tavi Gevinson, a 17-year-old who runs Rookie, an online fashion magazine, from her bedroom when she's not at school. It's hard, in other words, to join the counterculture when there's no culture. "There's not this us-vs.-them thing now. Maybe that's why millennials don't rebel," she says.

There may even be the beginning of a reaction against all the constant self-promotion. Evan Spiegel, 22, co-founder of Snapchat, an app that allows people to send photos, video and text that are permanently erased after 10 seconds or less, argues that it's become too exhausting for millennials to front a perfect life on social media. "We're trying to create a place where you can be in sweatpants, sitting eating cereal on a Friday night, and that's O.K.," he says.

But if you need the ultimate proof that millennials could be a great force for positive change, know this: Tom Brokaw, champion of the Greatest Generation, loves millennials. He calls them the Wary Generation, and he thinks their cautiousness in life decisions is a smart response to their world. "Their great mantra has been: Challenge convention. Find new and better ways of doing things. And so that ethos transcends the wonky people who are inventing new apps and embraces the whole economy," he says. The generation that experienced Monica Lewinsky's dress, 9/11, the longest wars in U.S. history, the Great Recession and an Arab Spring that looks at best like a late winter is nevertheless optimistic about its own personal chances of success. Sure, that might be delusional, but it's got to lead to better results than wearing flannel, complaining and making indie movies about it.

So here's a more rounded picture of millennials than the one I started with. All of which I also have data for. They're earnest and optimistic. They embrace the system. They are pragmatic idealists, tinkerers more than dreamers, life hackers. Their world is so flat that they have no leaders, which is why revolutions from Occupy Wall Street to Tahrir Square have even less chance than previous rebellions. They want constant approval--they post photos from the dressing room as they try on clothes. They have massive fear of missing out and have an acronym for everything (including FOMO). They're celebrity obsessed but don't respectfully idolize celebrities from a distance. (Thus Us magazine's "They're just like us!" which consists of paparazzi shots of famous people doing everyday things.) They're not into going to church, even though they believe in God, because they don't identify with big institutions; one-third of adults under 30, the highest percentage ever, are religiously unaffiliated. They want new experiences, which are more important to them than material goods. They are cool and reserved and not all that passionate. They are informed but inactive: they hate Joseph Kony but aren't going to do anything about Joseph Kony. They are probusiness. They're financially responsible; although student loans have hit record highs, they have less household and credit-card debt than any previous generation on record--which, admittedly, isn't that hard when you're living at home and using your parents' credit card. They love their phones but hate talking on them.

They are not only the biggest generation we've ever known but maybe the last large birth grouping that will be easy to generalize about. There are already microgenerations within the millennial group, launching as often as new iPhones, depending on whether you learned to type before Facebook, Twitter, iPads or Snapchat. Those rising microgenerations are all horrifying the ones right above them, who are their siblings. And the group after millennials is likely to be even more empowered. They're already so comfortable in front of the camera that the average American 1-year-old has more images of himself than a 17th century French king.

So, yes, we have all that data about narcissism and laziness and entitlement. But a generation's greatness isn't determined by data; it's determined by how they react to the challenges that befall them. And, just as important, by how we react to them. Whether you think millennials are the new greatest generation of optimistic entrepreneurs or a group of 80 million people about to implode in a dwarf star of tears when their expectations are unmet depends largely on how you view change. Me, I choose to believe in the children. God knows they do.

The original version of this article said that Jean Twenge is a professor at the University of San Diego. Twenge is a professor at San Diego State University.