The Illusion of Stock-Picking Skill

Key Insight

The stock market industry, where billions of shares are traded daily, appears to operate largely on an illusion of skill. Buyers and sellers, despite often having the same information, exchange stocks because they believe they know more about the correct price than the market does. Standard economic theory suggests that if assets are correctly priced, no one can consistently profit from trading, yet many individual investors lose consistently.

Research by Terry Odean, analyzing 10000 individual investor brokerage accounts over seven years (nearly 163000 trades), revealed that, on average, the stocks individual traders sold outperformed the stocks they bought by a substantial 3.2 percentage points per year, not accounting for transaction costs. Further studies showed that the most active traders achieved the poorest results, and men, who traded more on their 'useless ideas,' had worse investment outcomes than women.

Individual investors often make mistakes like selling 'winners' (stocks that have appreciated) and holding onto 'losers,' even though recent winners tend to continue performing well in the short term. They also tend to buy stocks simply because they are in the news. While professional investors are more selective, few, if any, stock pickers consistently beat the market. The evidence from over 50 years of research on mutual funds indicates that typically at least two out of every three funds underperform the overall market annually, and year-to-year correlations in their performance are negligible, suggesting stock selection is largely a game of chance rather than skill.