How we change what others think, feel, believe and do
A few vivid and memorable events occur (even just one). These are taken as proof that the event happens more often than it actually does. The pattern is as follows:
A gruesome night-time murder is covered in the news. People listening become worried and fewer people go out at night, to the extent that restaurants notice a drop in takings.
A student knows several people who got jobs easily after college. They assume they will also get a job without much effort. The student is surprised when they find jobs are not easy for them to to get.
A few people are found to be cheating in order to get state benefits. This is played up in a TV exposé and is subsequently taken as proof that there is a 'benefits culture' and that most people on benefits do not deserve such support.
The way that this fallacy works is that there is a confusion between recall and occurrence. When an event comes to mind a number of times, each remembering appears as a separate occurrence of the event (even if the person knows well that the event happens infrequently). This biases the person's estimation of probability.
This effect appears in decision errors when the availability heuristic is applied. It may also be seen in sayings such as 'One swallow does not make a summer' (the swallow bird migrates to the UK for the summer season).
After the 9/11 disaster in New York, the pictures of the towers collapsing were shown so often that some people (and particularly children) thought that many towers were collapsing. Fear of further terrorist attack increased massively and much more was spent on security in many areas.
This type of decisions is often one where there is a low probability of an event, but where the occurrence of the event would be disastrous or otherwise very unwelcome (sometimes called a 'Black Swan' event). In considering the decision, the anticipated pain of the possible event overwhelms the fact of the low probability.
A reversal of this is also possible, where the desirability of the event makes it seem more likely than in fact it actually is. This is an effect that gamblers face when they believe they are more likely to win than they actually are.
Misleading vividness plays to hope, where the person translates the hope for an event to happen (or not) into a probability of the event.