Availability Heuristic refers to a common mistake that our brains make by assuming that the examples which come to mind easily are also the most important or prevalent things.

For example, in the book Factfulness, by Anna Rosling Rönnlund, Hans Rosling, and Ola Rosling, they write that we are currently living in the least violent time in history. There are more people living in peace right now than ever before; the rates of homicide, rape, sexual assault, and child abuse are all falling.

Most people are shocked when they hear these statistics. Some still refuse to believe them. If this is the most peaceful time in history, why are there so many wars going on right now? Why do we hear about rape and murder and crime every day? Why is everyone talking about so many acts of terrorism and destruction?

The answer is that we are not only living in the most peaceful time in history, but also the best reported time in history. Information on any disaster or crime is more widely available than ever before. A quick search on the Internet will pull up more information about the most recent terrorist attack than any newspaper could have ever delivered 100 years ago.

The overall percentage of dangerous events is decreasing, but the likelihood that you hear about one of them (or many of them) is increasing. And because these events are readily available in our mind, our brains assume that they happen with greater frequency than they actually do.

We overvalue and overestimate the impact of things that we can remember and we undervalue and underestimate the prevalence of the events we hear nothing about.