Traders tend to fall prey to their wish to win. They overestimate the value of having this time a winning trade vs hitting sometimes big.

George Soros: It doesn't matter how often you are right or wrong - it only matters how much you make when you are right, versus how much you lose when you are wrong.

Someone else called this the Babe Ruth Effect. Few home runs can compensate for many strikouts. His lifetime batting average was only 0.342.

Psychologists Tversky and Kahneman: People choose a sure gain over a lottery with an expected better gain, but shun a sure loss over a lottery with a worse expectation.

William Eckhardt: People take profits, but gamble with their losses. Amateurs go broke by taking large losses, professionals by taking small profits.

Old market wisdom which directly results in only a few big winning trades and many small losses: Ride your winners, cut your losers

Trend Followers who run automated trading systems win only on average 40% of the time.