Most people think of the “mentally disordered” as a delusional lot, holding bizarre and irrational ideas about themselves and the world around them. Isn’t a mental disorder, after all, an impairment or a distortion in thought or perception? This is what we tend to think, and for most of modern psychology’s history, the experts have agreed; realistic perceptions have been considered essential to good mental health. More recently, however, research has arisen that challenges this common-sense notion.

In 1988, psychologists Shelly Taylor and Jonathon Brown published an article making the somewhat disturbing claim that positive self-deception is a normal and beneficial part of most people’s everyday outlook. They suggested that average people hold cognitive biases in three key areas: a) viewing themselves in unrealistically positive terms; b) believing they have more control over their environment than they actually do; and c) holding views about the future that are more positive than the evidence can justify. The typical person, it seems, depends on these happy delusions for the self-esteem needed to function through a normal day. It’s when the fantasies start to unravel that problems arise.

Consider eating disorders, for instance. It’s generally been believed that an unrealistically negative body image is an important factor in the self-abuse that characterizes anorexia and bulimia. A 2006 study at the University of Maastricht in the Netherlands, however, came to a very different conclusion. Here, groups of normal and eating disordered women were asked to rate the attractiveness of their own bodies. They were then photographed from the neck down, and panels of volunteers were brought in to view the photos and rate the women’s appearances objectively. The normal women, as it turned out, evaluated themselves much more positively than the panels did, while the self-ratings of the eating disordered women were in close agreement with the objective ratings. The eating disordered subjects, in other words, had a more realistic body image than the normal women. However, it is important to note that the study was based upon the broad concept of “attractiveness” rather than body weight specifically—while the eating disordered women may have rated themselves poorly because they felt “fat,” their weight was a controlled variable and not the basis of the volunteers’ assessments.

Studies into clinical depression have yielded similar findings, leading to the development of an intriguing, but still controversial, concept known as depressive realism. This theory puts forward the notion that depressed individuals actually have more realistic perceptions of their own image, importance, and abilities than the average person. While it’s still generally accepted that depressed people can be negatively biased in their interpretation of events and information, depressive realism suggests that they are often merely responding rationally to realities that the average person cheerfully denies.

Lear's Fool speaks wisdom disguised as madnessLear's Fool speaks wisdom disguised as madnessThose with paranoid disorders can sometimes possess a certain unusual insight as well. It has often been asserted that within every delusional system, there exists a core of truth—and in their pursuit of imagined conspiracies against them, these individuals often show an exceptionally keen eye for the real thing. People who interact with them may be taken aback as they find themselves accused of harboring some negative opinion of the person which, secretly, they actually do hold. Complicating the issue, of course, is the fact that if the supposed aversion didn’t exist before, it likely does after such an unpleasant encounter.

As one might imagine, these issues present some problems when it comes to treatment. How does one convince a depressed person that “everything is all right” when her life really does suck? How does one convince an obsessive-compulsive patient to stop religiously washing his hands when the truth of what gets left behind after “normal” washing should be enough to make any sane person cringe? These problems put therapists in the curious position of teaching patients to develop irrational patterns of thinking—patterns that help them view the world as a rosier place than it really is. Counterintuitive as it sounds, it’s justified because what defines a mental disorder is not unreasonable or illogical thought, but abnormal behaviour that causes significant distress and impairs normal functioning in society. Treatment is about restoring a person to that level of normal functioning and satisfaction, even if it means building cognitions that aren’t precisely “rational” or “realistic.”

It’s a disconcerting concept. It’s certainly easier to think of the mentally disordered as lunatics running about with bizarre, inexplicable beliefs than to imagine them coping with a piece of reality that a “normal” person can’t handle. The notion that we routinely hide from the truth about ourselves and our world is not an appealing one, though it may help to explain the human tendency to ostracize the abnormal. Perhaps the reason we are so eager to reject any departure from this fiction we call “normality” is because we have grown dependent on our comfortable delusions; without them, there is nothing to insulate us from the harsh cold of reality.

Christopher S. Putnam is a writer and bomb-disposal expert for the Damn Interesting A-Team. He posts from an undisclosed location in Saskatchewan, Canada.