Cognitive Biases

• Recency effect: People tend to overweight recent events in considering the probability of future events. In 2001, I would have rated the risk of another big terrorist attack on the US in the next two years as pretty high. Now I rate it as much lower. Yet the probability of a major terrorist attack is not really very dependent on whether there has been a recent successful one; it's much more dependent on things like the availability of suicidal terrorists, and their ability to formulate a clever plan. My current assessment is not necessarily any more accurate than my 2001 assessment, but I nonetheless worry much less about terrorism than I did then.

• Bandwagon effect: People tend to believe that something is a better idea if a lot of other people are doing it. In essence, they are trying to free ride on other people's analysis, on the assumption that someone must have thought this thing out. This has its uses--we don't all need to learn every hard lesson for itself. But in markets it produces herding behavior, which makes outcomes more extreme on both the upside and the downside. In other words, we get booms and busts. In the professional world, this is exacerbated by the fact that you're less likely to get fired if you fail at the same time everyone else does.
• Availability heuristic: People tend to overweight data that comes easily to mind, which is to say vivid (extreme) and recent examples.
• Beneffectance: People tend to view success as a result of their own actions, while they view failures as having been due to factors largely outside of their control.
  
• Confirmation bias: The tendency to look for data that confirms your theory, rather than data that falsifies it. Yes, we all know how this works in politics, but it's a much broader problem. People will repeatedly devise tests that give positive proofs of their theories, but much less often devise tests to falsify them.
• Hyperbolic discounting: People value small short-term payoffs more than much higher long-term payoffs.
• Optimistic bias: People tend to be overconfident about their own abilities and the outcome of their plans. Something like 90% of people think that they are above average drivers less likely to get into an accident than the average joe. This is so pervasive that there is actually a scientific name for the few people who accurately assess their own future, their abilities, and what other people think of them: clinically depressed.
• Overconfidence bias: Relatedly, people are too confident in the accuracy of their predictions. When asked to estimate a range of possibilities where the true outcome is 95% likely to fall within that range, people's guesses are wrong 40% of the time.