On October 5, 2006, the BBC reported that the second most senior leader of terrorist organization Al-Qaeda, Abu Ayyab Al-Masri, was killed in a raid in Haditha, Iraq. This event would have been a crowning achievement for global anti-terrorism efforts, except that Al-Masri was not in fact dead. The international media and U.S. military forces were mistaken about Al-Masri’s whereabouts in the raid. Proving to be a slippery and elusive figure, Al-Masri was declared dead at least once more on May 6, 2007 by The Economist, and then most recently in April 2010 by numerous reputable newspapers and websites. This failure of major media sources and military intelligence points to humans’ pervasive susceptibility to misbelief; and in matters far more mundane than the death of a top terrorist official, misperceptions of the truth plague our daily lives.

False beliefs carry a bad reputation for bringing turmoil and misunderstanding. No less an enlightened thinker than Thomas Jefferson noted, “It is always better to have no ideas than false ones; to believe nothing, than to believe what is wrong.” Mistaken beliefs can mean the difference between war and peace in the case of conflicts such as the Cuban Missile Crisis or the more recent pursuit of weapons of mass destruction in Iraq. Even common, small mistaken beliefs come with severe consequences like misbeliefs about appointment times that result in missed flights, missed jobs, and missed opportunities.

More recently, however, in an issue of Behavioral and Brain Sciences, psychologist Ryan McKay and philosopher Daniel Dennett posed the question of whether it can ever be right to be wrong. They argued that false beliefs can be good for you, in at least one particular way. McKay and Dennett systematically assessed a variety of different types of false beliefs—from pathological delusions to biased approximations of facts—for evolutionary value. Misbelieving that everyone is out to get you, for example, would not be adaptive for human survival because it impedes the ability to establish close relationships with others. Misbelieving that simply wearing a copper amulet will cure an illness when medicine is readily available is similarly maladaptive to staying alive.

McKay and Dennett concluded that only one mistaken belief passes muster, something that they called “positive illusions.” Positive illusions refer to unrealistically positive views of oneself, unrealistically positive optimism toward the future, and unrealistic views of personal control. McKay and Dennett argue that positive illusions are adaptive because they not only enhance psychological well-being—who doesn’t enjoy thinking of themselves as better than others—but because they enhance physical health as well.

A body of research spearheaded by psychologist Shelley Taylor and colleagues over the past 25 years consistently demonstrates a relationship between positive illusions and benefits to physical health including recovery from disease. Taylor’s work has shown that HIV-positive individuals with unrealistically positive views of their health outcomes survived longer and showed a slower illness course. In a similar set of studies, Taylor conducted extensive interviews with breast cancer patients and showed that those who fared the best with the disease were those whose positive illusions allowed them to attain a sense of meaning, a sense of mastery, and a positive view of themselves. Such findings are not to suggest that receiving a diagnosis for a fatal disease should immediately be cause for smiling and celebration. Indeed, it can be tremendously difficult to find optimism in dire circumstances: Author Barbara Ehrenreich described frustration with receiving advice to consider her own breast cancer diagnosis as a “gift” rather than a problem, in her recent screed against positive thinking, Bright-Sided. Nonetheless, a significant body of psychological research supports a relationship between positive thinking and positive health outcomes.

Positive illusions work their magic through a variety of psychological mechanisms, even directly influencing physiological and neuroendocrine response as well. Taylor’s work has shown that people who typically engage in unrealistic self-enhancement also showed lower cardiovascular responses to stress, more rapid cardiovascular recovery, and lower levels of cortisol, a hormone associated with increased stress.

Despite the robust nature of findings on the benefits of unrealistic optimism, not everyone agrees that positive illusions are all that positive, and some psychologists argue they do more harm than good. Psychologist David Dunning, for one, wrote a response to McKay and Dennett’s article, noting that people smoke cigarettes while mistakenly believing they can avoid serious disease, and are overly optimistic that they alone are capable of handling their high blood pressure despite doctor’s orders toward a stricter diet. Summarizing his argument, Dunning asked whether one would agree or disagree with the following statement: “ When flying, I prefer my pilot to have an overconfident view of his or her ability to handle rough weather.”

Whereas some disagree with positive illusions’ adaptive value, others suggest that positive illusions are not the only category of misbelief valuable for human functioning and survival. In another response to McKay and Dennett, psychologists Josh Ackerman, Jenessa Shapiro, and Jon Maner note that negative beliefs (unrealistically pessimistic beliefs about oneself, the future, or one’s personal control) might be just as important in the context of close relationships and intergroup interactions. For example, in the context of relationships, there is a well-documented tendency for women to underestimate men’s interest in romantic commitment, a belief that actually leads men to expend more effort in courtship, thereby stabilizing the relationship.

In response to these critiques, Dennett and McKay concede that there may be situational variation in whether particular false beliefs are adaptive or not. What is undeniable is that misbelief, misunderstanding, and self-deception are unavoidable in daily life. The growing body of research on this topic suggests that we can understand that our inaccuracies, misbeliefs and errors may be healthy in certain circumstances, and that is a belief—whether illusory or not—that should provide comfort.

Are you a scientist? Have you recently read a peer-reviewed paper that you want to write about? Then contact Mind Matters co-editor Gareth Cook, a Pulitzer prize–winning journalist at the Boston Globe, where he edits the Sunday Ideas section. He can be reached at garethideas AT gmail.com