Final answer:
Many investors make the common error of trying to pick stocks that will gain a great deal in the future to become rich quickly, but historical data shows that the majority of investors perform worse than the market average. Mutual funds that attempt to outperform the market often underperform.
Step-by-step explanation:
The common error that many investors make is trying to pick stocks that will gain a great deal in the future in order to become rich quickly. However, historical data shows that the majority of financial investors do not outguess the market and end up performing worse than the market average. Many mutual funds that attempt to pick stocks that will outperform the market actually underperform. Even for average investors, the odds of outperforming full-time professionals are not very good.