Here is an interesting New Yorker article on why sometimes ignorance is literally a bliss. Many years of research by psychologists and economists reveal interesting insights on how most of us make irrational choices. The more interesting punch line is that the more educated and intelligent crowd tend to err more when faced with questions which aim to test cognitive biases ! But why? One of the explanations offered in the article was that people who are more self-aware tend to use more introspection when evaluating their decisions/answers. As some researchers argue, many times introspection perpetuates the problem instead of remedying it because such self-analysis usually leads to elaborate justifications that are not relevant after all.
Yet I believe that sometimes it is not overconfidence but insufficient confidence that leads to wrong decisions. Educated people are more prone to doubt their own answers/solutions also when all it takes to make the right call is blind self-confidence, and not some elaborate deliberation that often increases uncertainty we perceive about the correct answer and leads us astray.