Confidence is an essential ingredient of success

Confidence is an essential ingredient of success in a wide range of domains ranging from job performance and mental health to sports, business and combat

The overconfidence effect is a well-established bias in which someone's subjective confidence in their judgments is reliably greater than their objective accuracy, especially when confidence is relatively high. For example, in some quizzes, people rate their answers as "99% certain" but are wrong 40% of the time.

Overconfidence can be a good thing, perhaps by boosting ambition, resolve, and other traits, creating self-fulfilling prophecies.

But positive self-delusion can also lead to faulty assessments, unrealistic expectations, and hazardous decisions, making it a mystery why overconfidence remains a key human trait despite thousands of years of natural selection, which typically weeds out harmful traits over generations.

Men tend to exhibit more false optimism than women, a trait that can help in their two traditional evolutionary roles: fighting rivals and courting women. In both situations, men are partly evaluated by their degree of self-confidence, 

Some researchers have claimed that people think good things are more likely to happen to them than to others, whereas bad events were less likely to happen to them than to others.

Strikes, lawsuits, and wars could arise from overplacement. If plaintiffs and defendants were prone to believe that they were more deserving, fair, and righteous than their legal opponents, that could help account for the persistence of inefficient enduring legal disputes

Sources:
nature.com
digg.com/newsbar
overconfidence..
en.wikipedia