A paper in Nature makes the case for the positive aspect of over-confidence: it encourages action and decisive response; it is generally successful or adaptive; when it goes wrong, it goes very wrong.
The evolution of overconfidence : Nature : Nature Publishing Group:
This would be consistent with the behaviour that is mirrored in financial markets. The carry trade is such a confident trait. There is the belief that the exit can be achieved before the shock. This is generally successful, certainly more successful than the alternative strategy that would hold back and worry about the risk of a funding currency appreciation. Those who embark on the strategy make years of gains. Those who stay on the sidelines, lose out. When the hit happens, it is a shock that is explained away by specific circumstances. The over-confident are not blamed and the cautious and not proved 'right' in most cases.