I offer my list of Investors’ 10 Most Common Behavioral Biases.  There are a number of others, of course, and more will continue to be uncovered.  But I think that these are the key ones.  Your suggestions of important ones I have missed are welcome.

1. Confirmation Bias. We like to think that we carefully gather and evaluate facts and data before coming to a conclusion.  But we don’t. Instead, we tend to suffer from confirmation bias and thus reach a conclusion first.  Only thereafter do we gather facts and see those facts in such a way as to support our pre-conceived conclusions.  When a conclusion fits with our desired narrative, so much the better, because narratives are crucial to how we make sense of reality.
2. Optimism Bias.  This is a well-established bias in which someone’s subjective confidence in their judgments is reliably greater than their objective accuracy. Indeed, we live in an overconfident, Lake Wobegon world (“where all the women are strong, all the men are good-looking, and all the children are above average”).  We are only correct about 80% of the time when we are “99% sure.” Fully 94% of college professors believe they have above-average teaching skills (anyone who has gone to college will no doubt disagree with that). Since80% of drivers  say that their driving skills are above average, I guess none of them drive on the freeway when I do.  While 70% of high school students claim to have above-average leadership skills, only 2% say they are below average, no doubt taught by above average math teachers. In a truly terrifying survey result, 92% students said they were of good character and 79% said that their character was better than most people even though 27% of those same students admitted stealing from a store within the prior year and 60% said they had cheated on an exam. Venture capitalists are wildly overconfident in their estimations of how likely their potential ventures are either to succeed or fail. In a finding that pretty well sums things up, 85-90% of people think that the future will be more pleasant and less painful for them than for the average person.
3. Loss Aversion. We are highly loss averse.  Empirical estimates find that losses are felt between two and two-and-a-half as strongly as gains.  Thus the disutility of losing $100 is at least twice the utility of gaining $100. Loss aversion favors inaction over action and the status quo over any alternatives. Therefore, when it comes time for us to act upon the facts and data we have gathered and the analysis we have undertaken about them, biases 2 and 3 – unjustified optimism and unreasonable risk aversion – conflict. As a consequence, we tend to make bold forecasts but timid choices.  (more…)