(FORTUNE Magazine) – For two decades Julie Norem has worked to make it safe for the pessimists of America to come out of the closet. So far she has little cause for optimism. Only 10,000 copies of her 2001 book, The Positive Power of Negative Thinking, were sold before the hardcover edition was remaindered--that's less than 0.2% of the total sales to date of Norman Vincent Peale's peppy classic, The Power of Positive Thinking. Norem, a Wellesley College psychology professor, is also swimming upstream in academia. While the study of happiness is ascendant among U.S. psychologists, she focuses on anxious people who feel in their bones that Murphy's law describes a force of nature.

Unlike Norem, scholars of happiness find it almost deliriously easy to hit resonant chords in the American psyche. Their books, such as Learned Optimism by former American Psychological Association president Martin Seligman, become bestsellers. Their findings make news; a study concluding that Nigeria has more happy people per capita than any other nation recently generated worldwide headlines. They even have their own genius prize--the $100,000 Templeton Positive Psychology Award, established by philanthropist John Templeton, founder of the Templeton mutual fund group.

But if Norem is right, the sunny scientists have missed something: Putting on a happy face is a poor strategy for many people. Norem calls them defensive pessimists. Temperamentally given to angst, they typically begin a project by assuming things will go badly. Then they work through their anxiety--and often lay the groundwork for success--by carefully preparing to fend off the expected botches and bad luck. Norem's studies show that when such people are cajoled into don't-worry-be-happy mode, their performance actually goes downhill.

In her book Norem describes how a defensive pessimist she knows, a sociology professor, plans a retirement dinner for a colleague by anxiously quizzing herself about possible disasters: Will old professor Smith be able to hear if he's seated at the middle table? Can raffish professor Jones be trusted not to tell off-color jokes if allowed to give a toast? Will quarrelsome students be able to sit near each other without a blowup?

In contrast, says Norem, "strategic optimists" regard such obsessive worrying as weird. An upbeat architect she describes, for example, likes to gear up for major presentations to clients by shooting Nerf-ball hoops in his office. When he goes into the meeting, his jovial, self-confident demeanor usually carries the day.

Norem stresses that defensive pessimists aren't necessarily gloom-ridden. Their coping mechanism is a strategy, not an indelible personality trait, and they can switch to upbeat modes in situations that don't trigger their anxiety. But she concedes that they are usually in a worse mood than optimists. (To gauge your own level of defensive pessimism, surf to www.wellesley.edu/Psychology/Norem/Quiz/quiz.html.)

A chipper 43-year-old, Norem says she isn't down on optimism. In fact, she sees herself as tending toward the bright side. ("I've had to learn to be a defensive pessimist," she says, in order to manage a demanding career while rearing two kids.) And she agrees with a key point the positive psychologists never tire of making: Optimists are prone to happy, self-fulfilling prophecies.

Still, Norem takes issue with the positivists' one-size-fits-all message, to just say no to negativity. In one of her most telling studies, defensive pessimists were hooked up to equipment that measured physiological signs of anxiety, such as sweating, while preparing to take aptitude tests. Half the pessimists were allowed to do their usual thing--ruminate nervously about the trial to come. The other half were given a simple clerical chore that distracted them from anxious musing. The researchers found that the undistracted pessimists' anxiety peaked during their mental rehearsal, then fell just before and during the test. The second group's experience was the opposite--their anxiety fell while they were distracted but shot sky-high at test time, hurting their performance.

One defensive pessimist explained to Norem that adopting an upbeat outlook before a major challenge feels artificial and risky to him, and that when he does so, he winds up feeling panicky when the trying events are upon him.

Norem is at her most provocative when discussing her work's larger implications. Defensive pessimists are perennially undervalued in American society, she argues. Though they tend to be detail-oriented realists, "they're almost never seen in leadership positions." Instead they are typically found in jobs like secretary or nurse, which involve major responsibilities and little power--their knack for picturing what might go wrong is ideal for "covering their bosses' behinds" in such roles. It seems that more women than men are defensive pessimists, she adds, as surveys show that females feel more anxiety than males--or at least are more willing to admit self-doubt.

Defensive pessimists sometimes do achieve stardom in America, says Norem. Many famous entertainers, for instance, seem to be anxious people given to obsessive rehearsing. Woody Allen has made an art form of angst. Secretary of State Colin Powell, she adds, might be a "closet defensive pessimist"--a high-profile leader forced by his role to act more optimistic than he is.

But America has always been ruled by optimists, Norem says. The Pilgrim Fathers showed the way in 1620 with a bold leap of faith: They chose to sail forth in the Mayflower in the fall, of all seasons. As a result they landed in Massachusetts in the middle of winter, short on food. Half were dead within a year, many from starvation. But the power of their positive thinking never faded in the New World. Consider the fantastically rosy assumptions that the former CEOs of AOL and Time Warner used to justify merging the companies, or the Bush administration's confident shoving aside of doubts leading up to the Iraq invasion.

Norem cites such cases to illustrate one of her sharpest points: Optimists tend to live in a world of mild illusions. Full of happiness-abetting self-esteem, they typically attribute their successes to skill and their failures to bad luck. They often overestimate their ability to control things--optimists insist on picking their own lottery numbers rather than using ones randomly chosen by computer.

In an experiment, Norem and colleagues asked research subjects to describe themselves on camera, as if making a video for a dating service. The researchers then gave all the subjects identical mixed reviews, rating how attractive they were, how much they needed to improve, and the overall success of their performance. When later asked about the feedback, subjects categorized as strategic optimists (via a preadministered questionnaire) remembered their ratings as significantly more positive than they actually were. Subjects classified as defensive pessimists, on the other hand, tended to remember the feedback more accurately.

Pessimists, of course, are prone to distort reality in negative ways, especially when assessing themselves. But Norem notes that such illusions generally have little fallout compared with those of the upbeat powers that be, whose rosy distortions in the Nuclear Age can have global repercussions. "I wouldn't advocate that defensive pessimists run everything," she says. "But I would advocate that every decision process with important consequences should include a defensive pessimist." Maybe we'd all have more reason for optimism if that happy wish came true.

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