They are regularly accused of being too confident – even cocky – but the highest achievers are more often than not those who over-rate their ability.

他们经常因为太过自信甚至自负而遭到指责，然而成就最高的人往往是那些过高估计自身能力的人。

Now researchers believe they have discovered, for the first time, why humans have a false sense of optimism（乐观） .

Computer led simulations have shown that overconfidence in all aspects of life can often improve your chances of winning.

For many years scientists have been divided over whether overconfidence is a good or bad thing and why it existed.

'There hasn't been a good explanation for why we are overconfident, and this new model offers a kind of evolutionary¹ logic² for that. It's unlikely to be an accident—we're perhaps overconfident for a good reason,’ said Dr Dominic Johnson of the University of Edinburgh.

Sprinter³ Usain Bolt is famed for his relaxed and confident approach to performing, as was ‘the greatest’ boxer⁴ Muhammad Ali.

But there is a word of warning for anyone thinks they could be faster than a speeding bullet, more powerful than a locomotive（火车头） , or able to leap tall buildings in a single bound.

Positive self-delusion can also cause problems and lead to wrong decision making, unrealistic expectations, danger and failure.