This uncomfortable fact, which many economists have recently accepted, suggests that we are living not simply in an unequal society but rather in two separate, side-by-side economies. For those who can crack the top 20 percent, there is great promise. Most people in that elite group, Rank told me, will spend at least part of their careers among the truly affluent, earning more than $250,000 a year. For those at work in the much larger pool, there will be falling or stagnant wages and far greater uncertainty. A college degree is an advantage, but it no longer offers any guarantee, especially for those who graduate from lower-ranked for-profit schools. These days, a degree is merely the expensive price of admission. In 1970 only one in 10 Americans had a bachelor’s degree, and nearly all could expect a comfortable career. Today, about a third of young adults will earn a four-year-degree, and many of them — more than a third, by many estimates — are unlikely to find lifelong secure employment sufficient to pay down their debt and place them on track to earn more than their parents. If they want a shot at making it into the top 20 percent, they now need to learn a skill before they get a job. And for many, even with their parents’ help, that’s going to be an impossibility.

For all these grim forecasts, people now in their 20s are remarkably optimistic. Arnett, who recently conducted a nationwide poll of the group, discovered that 77 percent still believe they will be better off than their parents. A Pew survey found that only 9 percent of young adults believe they won’t be able to afford the lives they want. This combination of confidence in the face of historic uncertainty might seem confusing, but Arnett argues that optimistic boomerang kids might not be as blithely naïve as their parents imagine. Many are rejecting the Dilbertian goal of a steady, if unsatisfying, job for years of experimentation, even repeated failure, that eventually leads to a richly satisfying career. Sleeping in a twin bed under some old Avril Lavigne posters is not a sign of giving up; it’s an economic plan. “Stop dumping on them because they need parental support,” Arnett cautioned. “It doesn’t mean they’re lazy. It’s just harder to make your way now than it was in an older and simpler economy.”

Adrianne Smith, 28, graduated from the University of Central Florida in 2008 and went to work as a behavioral analyst treating children on the autism spectrum. She was quickly making more than $60,000 a year, but in order to earn that money, “I had a huge caseload,” she said, handling 25 clients while paying off more than $40,000 in student loans. She knew of therapists earning $100,000 annually, but they did so by handling 40 or more physically and emotionally demanding cases.

So Smith came up with a more efficient idea. After doing some research on local clinics, she noticed that a rise in autism diagnoses mirrored the rising demand for clinic services. And with the convenience of modern technology, from smartphones to their attendant payment readers, she could build a clinic serving clients in their homes, one that could be leveraged into a larger regional network. With a bit of hustle, Smith thought, she could set herself up with a profitable business that would give her returns for the rest of her life. To afford the start-up costs, she moved back in with her parents, turned her sister’s old room into an office where she could work and store toys for her clients, and used what would have been rent money to develop a website and hire a few part-time therapists to make house calls. “I couldn’t have opened a clinic without my parents’ support,” she said. Now when Smith meets peers who deride her for living at home, she replies that it’s really just a business incubator.

I wasn’t surprised that Arnett was impressed by Smith’s plan. But I didn’t expect him to praise Kasinecz too. At 27, she had a lot of debt, no career in mind and a series of unsatisfying jobs. I worried that her prospects were dimming, that crossing that 20 percent threshold would seem harder and harder with each passing year. She seemed worried, too. “We’re kind of in this limbo phase where we’re expected to be these great professionals who come out of college with bomb-ass jobs,” she said of her generation. “And then we’re like, Wait. I’ve got 80 grand in debt. How am I supposed to do that?”

Arnett told me, however, that I wasn’t seeing her hidden strengths. In fact, he would be far more worried if she had done what the previous generations did — stayed in whatever job she took after graduating, no matter how little she liked it — or if she were similarly underemployed but expressed no urgency about finding a better job. Kasinecz, he said, was still searching for the right fit and refusing to settle for anything less. Somewhat counterintuitively, Arnett said, it’s the people most actively involved in this struggle, the ones who at times seem totally lost, who are likely to find their way. Kasinecz seemed to know this, too. And in that sense, she was emblematic of a generation in which there are no more average workers and even less certainty. Kasinecz may well find a job she likes and, eventually, the right career — even if she terrifies her mother, herself and a few hand-wringing economists in the process.