One that gets just about everybody, including me, is the Availability Heuristic. That’s estimating the prevalence of something based on how easy it is to remember examples of it. Like, for instance, crime. It’s hard to compare the number of criminal acts to the size of the population to get a true picture of how prevalent crime is. It takes a lot of mental effort, so our brains just estimate it based on the number of incidents we’ve heard of using the heuristic that something must be more common if we can recall more examples of it.

That’s why Americans in general think that violent crime is exploding, despite it actually being way down over past decades. The 24-hour news channels fill airtime and the Internet brings us the aggregated crimes of a whole nation, so it’s easy to remember lots of instances. Meanwhile, we don’t worry about heart disease, it doesn’t feel prevalent by comparison, because it doesn’t make the news, and we don’t have easy recall of all the heart attack deaths every day.