The Perils of Investor Overconfidence

By Whitney Tilson September 20, 1999 But humans are not just robustly confident-they are wildly overconfident.

Consider the following:

- 82% of people say they are in the top 30% of safe drivers;
- 86% of my Harvard Business School classmates say they are better looking than their classmates (would you expect anything less from Harvard graduates?);
- 68% of lawyers in civil cases believe that their side will prevail;
- Doctors consistently overestimate their ability to detect certain diseases (think about this one the next time you're wondering whether to get a second opinion);
- 81% of new business owners think their business has at least a 70% chance of success, but only 39% think any business like theirs would be likely to succeed;
- Graduate students were asked to estimate the time it would take them to finish their thesis under three scenarios: best case, expected, and worst case. The average guesses were 27.4 days, 33.9 days, and 48.6 days, respectively. The actual average turned out to be 55.5 days.
- Mutual fund managers, analysts, and business executives at a conference were asked to write down how much money they would have at retirement and how much the average person in the room would have. The average figures were $5 million and $2.6 million, respectively. The professor who asked the question said that, regardless of the audience, the ratio is always approximately 2:1.

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