Area Yuo Stoopid
A study shows that if you are an idiot, you likely don't know it, and never will unless you get smart all of a sudden!
It seems that the reason for this phenomenon is obvious: The more incompetent someone is in a particular area, the less qualified that person is to assess anyone's skill in that space, including their own. When one fails to recognize that he or she has performed poorly, the individual is left assuming that they have performed well. As a result, the incompetent will tend to grossly overestimate their skills and abilities.
The article is over a year old, and the study a few years old, but it likely still holds its water.