This article serves as a concise primer on behavioral finance, documenting a wide range of systematic mistakes that cause investors to underperform.

The evidence shows that investors fail to diversify, mistime fund investments, trade excessively due to overconfidence, chase past returns, and exhibit well-known biases such as the disposition effect, home bias, and attention neglect. Investor trades are also highly correlated, amplifying losses rather than diversifying risk.

Overall, the article highlights that poor performance is rarely due to a lack of available information or investment opportunities, but rather to persistent behavioral errors.