Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in anyway.
From the always amusing Megan McArdle:
People tend to be overconfident about their own abilities and the outcome of their plans. Something like 90% of people think that they are above average drivers less likely to get into an accident than the average joe. This is so pervasive that there is actually a scientific name for the few people who accurately assess their own future, their abilities, and what other people think of them: clinically depressed.