I've always been a night owl. Even as a child and teenager I often went to bed late, much to my father's frustration. He was fully convinced that I was damaging my health because of it. One time my dad took me to the doctor because I had the flu. At the doctor's office my dad commented about my habit of going to bed late, which to him obviously contributed to my illness. The doctor explained that as long as I got enough sleep, staying up late isn't really a big deal, and had nothing to do with me being sick. You can imagine the smirk on my face after the doctor left the room. After a moment of silence, my dad remarked, "Oh, what does he know anyway?"

Why would my father, who never studied medicine, stubbornly conclude that he still knew more about human health than someone who has spent decades in that profession? Social psychologists Carol Tavris and Elliot Aronson argue that it's due to cognitive dissonance, a psychological term describing the internal conflict that ensues when someone holds two polarizing beliefs, or when that person's behavior goes against a particular belief. In their book Mistakes Were Made (But Not by Me): Why We Justify Foolish Beliefs, Bad Decisions, and Hurtful Acts, the authors explore people's strong need for self-justification and the sometimes serious consequences.

Alexander Pope once said, "To err is human, to forgive divine." Indeed, we make many mistakes and often own up to them. However, what Pope didn't realize is that humans also have a strong sense of self-preservation. People tend to view themselves in a positive light — as intelligent, rational, respectable, and good human beings. When a person does something that goes against their beliefs, their self-concept is threatened, creating cognitive dissonance. To maintain that positive view of the self, the person then justifies that behavior. For example, although many overweight people are aware of the dangers to their health, they often tell themselves that they're too busy and don't have time to exercise; that they're entitled to eat what they want; or that they may be fat, but they're not that fat. In doing so, they regain their positive self-concept.