Why are people overconfident so often? #behaviour

Why are people overconfident so often? (8/18/2012): Researchers have long known that people are very frequently overconfident - that they tend to believe they are more physically talented, socially adept, and skilled at their job than they actually are. For example, 94% of college professors think they do above average work (which is nearly impossible, statistically speaking). But this overconfidence can also have detrimental effects on their performance and decision-making. So why, in light of these negative consequences, is overconfidence still so pervasive?