Why the average investor underperforms almost every asset class

The average investor underperformed nearly every asset class, including even government bonds:

Source

The reason is emotional (inconsistent) behavior of average investor:

expecting to find high returns with low risk, when returns, actually, depend on risk taken,copying the behavior of others (“herding”),treating errors of commission more seriously than errors with omission,tendency to react to news without quantitative examination,belief that good things happen to me, and bad things happen to ot...