Here's an excerpt:
The researchers from University of Edinburgh and University of California, San Diego, simulated the effects of overconfidence over generations, using a mathematical model. They compared the outcomes of overconfident strategies against accurate and under-confident strategies, and found that being overconfident frequently works to one’s advantage, as long as the rewards outweigh the risks. People with unbiased, accurate perceptions, on the other hand, usually fare worse, UPI says.
The research suggests that over time, natural selection favours those who have an overly positive self-image over those who are insecure.