The idea of “positive illusions” is one that has been popular in social psychology since Taylor and Brown published their 1988 paper, “Illusion and well-being: A social psychological perspective on mental health.” Simply put, positive illusions are biased perceptions of reality that are thought to be good for mental health.
For instance, studies have shown that people perceive themselves to be smarter, more attractive, and more virtuous than other people, and these overly optimistic perceptions also extend to relationship partners. Likewise, I probably think my husband is way more attractive than other people think he is (they’re wrong, I’m right, obviously). Most importantly, many of these studies have shown that people who use positive illusions are happier and healthier than those who don’t. However, not all studies show this effect. It stands to reason that seeing the world in a completely biased way can’t be good for you. So when should we try to see the world through positively biased lenses and when should we try to see things more realistically? 

Recent research published by O’Mara, McKnulty, and Karney (2011) in the Journal of Personality and Social Psychology attempts to answer this question. Using interviews conducted with newly married couples, they looked at the spouse’s perceptions of their stressful experiences, the degree to which those perceptions were positively biased, and how mental health and future outcomes were affected. They found that positive bias in the perception of stressful experiences was only helpful when those stressful experiences were not TOO severe. When stressful experiences were particularly severe, positive bias was not helpful. The authors predict that positive bias in the case of severe stressful experiences causes you to avoid taking care of the experience. Thus, things just get worse, causing negative consequences for mental health and future outcomes.

In summary, the lesson here seems to be the old adage: don’t sweat the little things. However, you might want to sweat the big things.