" ...maybe a better question about confidence - financial and otherwise - is not why people are overconfident to begin with, but why they stay overconfident. You see, the problem with overconfidence is not the innate bias toward optimism that most people seem to possess. That's a good thing, it keeps the world moving forward. The problem is the inability to temper optimism as a result of prior experience. Frankly, we don't learn well enough from our mistakes. Consider: If overconfidence is as big a problem as we say it is, it should be a short-term problem at worst. The learning process would ideally go something like this: We think highly of ourselves, the world and events show us who is the boss, and we become less confident and more realistic about our knowledge and skills. Yet in the main, this does not happen."
Belsky & Gilovich, authors: Why Smart People Make Big Money Mistakes