My usual reaction is to scowl. I'm as happy as the next person (that is, moderately happy most of the time, psychologists report). But I don't like being commanded to be positive—all the time and no matter the circumstances. Sometimes, smiles just aren't what a situation demands.

Yet in recent years it feels like we've all been ordered to "think positive" by an army of experts in any number of fields. Doctors inform us that optimism improves our health and helps us live longer, reduces the risk of stroke, even. Corporate coaches advise us that employees earn more money and climb the ladder more quickly. " " researchers broadcast studies showing that optimistic people are happier and have more friends. In every way, it seems, optimists bask in the sunshine of the world's approbation, while pessimists mope in the shadows.

"It's gotten to the point where people really feel pressure to think and talk in an optimistic way," observes B. Cade Massey, an assistant professor of organizational behavior at the Yale School of . Massey's research shows that, when asked to forecast the outcomes of events like a financial investment or a surgical procedure, study subjects make predictions that they know are overly optimistic. Yet they also say they wish to be even more optimistic than they already are. Clearly, many of us have drunk the optimism Kool-Aid: We view optimism as an unqualified good, an all-purpose remedy for everything that ails us.

But a more nuanced view is emerging from the lab. Researchers find that optimism and pessimism operate not only as fixed points of view but also as mind-sets we can adopt as needed, rose- or blue-tinted lenses that we can put on and take off depending on the situation. Such a targeted use of optimism may actually be more effective than a blanket policy of all optimism, all the time.

Psychologists are even daring to challenge the preeminence of optimism as our most sought-after state of mind. While not confusing America with, say, France, they contend that pessimism also has documentable virtues. "In America, optimism has become almost like a cult," says Aaron Sackett, a psychologist at the University of St. Thomas in Minneapolis. The faith we place in is not merely naíve but fails to capture the complexities of human .

Strategic optimism and pessimism, on the other hand, are more difficult to investigate precisely because they depend on specific situations. Harder to capture, they have eluded investigation. "But," says Chang, "the field is starting to recognize that many of us use these mind-sets in a flexible way and that this flexibility has a lot of advantages."

At the same time, optimism's poor relative, pessimism, is emerging from the shadows. "In this country, pessimism comes with a deep stigma," notes the Michigan psychologist. Take the study that asked subjects to read descriptions of two people, one optimistic and one pessimistic, and to imagine meeting them. Subjects predicted they would like the optimist and said they would not want to talk to the pessimist, that he would not be very friendly or sociable—that he was probably depressed!

For Americans, longtime adherents of the positive-thinking doctrine, pessimism means being a gloomy, dreary, sad-sack loser. But that's not necessarily so. Successful people often employ pessimism in a strategic way to motivate and prepare themselves for the future, recent research indicates. It's simply not the case that optimism is "good" and pessimism is "bad"—although that's how we've been encouraged to think about them. Rather, both are functional. And both have value.

If both optimism and pessimism are functional, you may be wondering just what is it that they do. "Optimism and pessimism are feelings about the future," explains Yale's Massey. "They help us manage our expectations and our actions moving forward."

Because the world is unpredictable, we continually generate mental scenarios about how we think things will unfold, and we color these scenarios bright or dark, hopeful or fearful. Why not make our forecasts neutral—neither optimistic nor pessimistic but simply realistic? It turns out that optimism and pessimism are not distortions or flaws in our vision (at least, not always), but in fact are enhanced perspectives that give us something more than mere realism can provide.

Both optimism and pessimism, for example, can act as powerful motivators. If you realistically considered how much risk you were taking on with a new project or acknowledged how much work it would demand, you might never make the attempt. But the energizing force of optimism can convince you it will work out just long enough to turn that prediction into a reality. Likewise, pessimism about a potential outcome can mobilize us to act with alacrity: There's nothing like a looming disaster to make us get things done. " The emotional component of optimism and pessimism is what makes them so influential," says David Armor, an assistant professor of psychology at Yale. "We can look ahead and anticipate in objective terms what's likely to happen. But optimism and pessimism bring feelings along with them, and those feelings push us into action more forcefully than any rational prediction could."

The feelings that come along with optimism and pessimism serve a second function: They help us manage other emotions that might get in the way of our effectiveness. Optimism, for example, can act as a bulwark against ; it fills us with an expansive sense of our own power to shape events, overruling the doubts and worries that might otherwise paralyze us into inaction. Optimism can also buoy us up when things go wrong; deluged by feelings of hopelessness and despair, optimism is the raft we cling to until the skies clear.

"Positive assumptions about the future may allow us to tolerate situations that would otherwise be unbearable," Armor notes. "An entrepreneur starting up a company, for example, might drive himself to work 18-hour days for months and even years because he optimistically believes that there will be a big payoff for him at the end."

Although pessimism may seem like an odd choice as an emotional helpmeet, it, too, can assist us in managing our feelings. By spinning down our expectations ("I probably won't get this prestigious award/coveted assignment/hot date"), it insulates us from crushing disappointment when things don't go our way. "Pessimism is an ego-protection strategy," notes Aaron Sackett. "If you're up for a promotion at work and optimistically believe that you'll get it, you'll have to absorb a big blow to your and when you don't receive it. If you adopt a pessimistic attitude about your chances, however, you won't be nearly so affected emotionally when you lose out as you had predicted."

The key to using optimism and pessimism strategically is to match the mind-set to the situation. When searching for a new job, for example, it's important to muster all the optimism we've got. A 2010 study by Cade Massey, conducted with Ron Kaniel and David Robinson of Duke University's Fuqua School of Business, reported that people who adopted an optimistic outlook were more likely to be quickly hired.

How does optimism exert such an effect? Massey proposes that it allows job seekers to deal more productively with the rebuffs they inevitably encounter. "They're not destroyed when setbacks occur, because they're choosing to believe that everything will eventually turn out fine," he says. "Optimism gives them the fortitude to keep going, when people who are pessimistic about their prospects might just give up."

Optimism also allows individuals to think more flexibly and creatively, Massey notes. "When you're engaged in an optimistic mind-set, your belief is that things will work out—you just need to figure out how," he says. "That attitude allows you to come up with innovative solutions, while a pessimistic outlook might just leave you stuck."

Another situation in which it's useful to don rose-tinted glasses: when you're embarking on a high-risk, high-reward enterprise, such as starting your own business or producing your own invention. Realistically speaking, the odds of success in such ventures are low. Data from the U.S. Census Bureau show that more than half of all new businesses fail within the first five years, and the U.S. Patent and Trademark Office is inundated every year with thousands of applications that are never approved. Yet every entrepreneur and inventor must believe that his or her project will be the one to defy the odds.

Optimism motivates people to work as hard as they possibly can on their long-shot ventures, and it buffers them from the ever-present risk of failure. Indeed, many studies have found that entrepreneurs are especially likely to adopt an optimistic outlook. They're overly confident about their own abilities and tend to draw very positive conclusions from limited data—mental habits that, while not entirely grounded in reality, may nonetheless spur on new business owners in the face of adversity.

Likewise, a 2007 study by University of Toronto management professor Thomas Astebro found that inventors are more overconfident and optimistic than the general population. More than half of the inventors studied continued to spend time on their projects even after receiving "highly diagnostic advice to cease effort." They kept going even after experts advised them to quit.

Even an ordinary effort like going on a diet can benefit from a dose of optimism, research finds. Here again, the odds are stacked against us. A comprehensive review of studies conducted by scientists at UCLA in 2007 found that, within four to five years, two-thirds of dieters gained back more weight than they initially lost. Given that dim outlook, optimism provides a much-needed boost: It convinces us that our weight-loss goal is achievable, it fortifies our resolve to resist temptations such as snacks and desserts, and it persuades us to climb back on the wagon when we've slipped—because, we optimistically believe, those pounds are simply bound to come off.

Indeed, a study by Yael Benyamini of Tel Aviv University in Israel found that dieters who demonstrated an optimistic attitude by setting higher weight-loss goals and expressing greater in the attainment of those goals actually did lose more weight. "Optimism can have a self-fulfilling aspect," notes Aaron Sackett of the University of St. Thomas. "In many situations, positive expectations lead to positive outcomes."

And pessimism? When is it useful? Surprisingly, it can be most helpful at the moments when we might seem to have the least to feel pessimistic about. When we've been successful before and have a realistic expectation of being successful again, we may be lulled into laziness and overconfidence. Pessimism can give us the push that we need to try our best. This phenomenon, known as "defensive pessimism," involves imagining all the things that might go wrong in the future. It spurs us to take action to head off the potential catastrophes we conjure and prevent them from happening. Individuals who employ such a tactic, researchers report, hardly fit the stereotype of sad-sack Eeyores moaning about the gloomy state of the world.

"The interesting thing about people who engage in defensive pessimism is that they tend to be quite dynamic and successful," says Lawrence Sanna, a professor of psychology at the University of Michigan. "They use the technique to motivate themselves to do the very best job they can."

An executive organizing a conference, for example, might anticipate a disagreement between two participants and arrange to seat them at opposite ends of the table. She might predict that attendees will get tired and hungry after several hours of discussion and plan for breaks and meals. And she might foresee that the meeting will end without any firm conclusions and therefore build a "Where do we go now?" final session into the schedule. If she'd adopted a breezy optimism ("Everything will go fine!"), the conference likely would not be as successful.

Pessimism can also be an effective motivator when we're faced with an overwhelming or amorphous . A feeling of foreboding about an outcome can prompt us to take necessary steps that we would otherwise avoid. In the wake of 9/11, for example, many Americans pessimistically predicted further attacks, but they dealt constructively with their worries by stocking up on canned goods, bottled water, flashlights, and batteries.

Today many Americans are pessimistic about the needed economic recovery. But reports show that as a result, they're making smart choices, such as saving money and investing for . Put to use in this fashion, pessimism isn't a lamentable drain on our time and energy but a productive strategy for dealing with uncertainty. "The phenomenon of defensive pessimism shows that there are times when pessimism and are actually features of a positive psychology, since they lead to better performance and personal growth," says Michigan's Edward Chang.

Pessimism can also provide assistance when our fears are more concrete and immediate—when we think we're about to receive bad news, for example. Kate Sweeny, an assistant professor of psychology at the University of California, Riverside, has found that bracing ourselves for a negative outcome has a positive psychological effect. "When you finally get the bad news, you still feel bad, but not as bad as if you never saw it coming," says Sweeny. "You've had a chance to work through the emotional implications of this negative event in advance. You may even have put some supports in place—bringing a friend along to a doctor's appointment, perhaps, to help you cope with a worrisome diagnosis, or lining up a tutor if you know you've failed an important exam."

And in the face of an objectively grim reality—when the news is bad and likely to get worse—pessimism is an ally. A recent study published in The International Journal of Aging and Human Development reported that elderly people who are realistic and even pessimistic about the likelihood of experiencing negative life events—such as the approaching deaths of close friends and relatives—are actually less vulnerable to than elderly people who are more optimistic. In their case, a dose of pessimism offers protection against the fresh pain of loss.

The turn away from one-size-fits-all optimism, says Michigan's Lawrence Sanna, reflects a pendulum swing within the field of mental health. For much of the 20th century, psychologists focused almost exclusively on pathology and dysfunction, he notes. "The positive psychology movement came about in reaction to that. Now we're realizing that and optimism are not a complete answer, either."

Such shifts in emphasis have also tracked the mood of the culture at large. The ideas behind positive psychology had been percolating for several years before 1998, when University of Pennsylvania psychologist Martin Seligman chose positive psychology as the theme of his term as president of the American Psychological Association. Its upbeat message jibed perfectly with the expansive mood of that prosperous, peaceful decade.

Today, of course, our frame of mind is very different. Two wars that don't seem to end, an economic recovery that can't get going, hard choices on every front—all these developments shape a decidedly un-rah-rah mood. Appreciating the value of pessimism and the careful, restrained use of optimism seems consonant with the sometimes painful downward ratcheting of expectations we are collectively undergoing.

The social critic Barbara Ehrenreich heralded the rethinking of mindless optimism in her 2009 best-seller, Brightsided: How Positive Thinking Is Undermining America. In recent years American optimism reached a crescendo. She blamed "the tyranny of positive thinking" and the nation's "reckless optimism" for both the war in Iraq and the economy's crash.

Ehrenreich, also the author of 2001's Nickel and Dimed: On (Not) Getting By In America, has long trained an eye on the underside of America's smiling surfaces. More surprising is that the founder of positive psychology himself, Martin Seligman, is now doing so, too.

Seligman put optimism on the intellectual map after his pioneering experiments in the 1970s showed that the ultimate negative mind-set, depression, was largely a consequence of " ." The opposite of this passive, defeated state is learned optimism, the gateway to optimal functioning and the title of his 1990 book, which vaulted onto the best-seller list. More recently, he authored the positive-psychology bible, Authentic Happiness.

Asked if optimism, like happiness, requires a reconsideration, Seligman demurs. "If anything, the evidence in support of the health benefits of optimism is now stronger than ever," he asserts. But, he acknowledges, common beliefs about optimism are due for a correction. "The idea that optimism is always good is a caricature. It misses realism, it misses appropriateness, it misses the importance of negative emotion."

Seligman is still an advocate of optimism. But he says it must be paired with "reality testing"— checking on the results of our efforts—to make sure that overly positive expectations are not leading us astray.

If even the father of positive psychology seems a bit less, well, positive these days, the rest of us could probably take a hard look at our own beliefs. Optimism has its uses, to be sure. But the goal to "think positive" no matter the situation is insupportable and counterproductive. A wiser aim is to find the most effective way to propel us where we want to go. Both optimism and pessimism can help us get there—smiley face not required.