Wikipedia:

The availability heuristic is a phenomenon (which can result in a cognitive bias) in which people predict the frequency of an event, or a proportion within a population, based on how easily an example can be brought to mind.

Have you read Thinking, Fast and Slow, by Daniel Kahneman?

Here's Freeman Dyson:

A striking example of availability bias is the fact that sharks save the lives of swimmers. Careful analysis of deaths in the ocean near San Diego shows that on average, the death of each swimmer killed by a shark saves the lives of ten others. Every time a swimmer is killed, the number of deaths by drowning goes down for a few years and then returns to the normal level. The effect occurs because reports of death by shark attack are remembered more vividly than reports of drownings. System One is strongly biased, paying more prompt attention to sharks than to riptides that occur more frequently and may be equally lethal. In this case, System Two probably shares the same bias. Memories of shark attacks are tied to strong emotions and are therefore more available to both systems.

Sharks Save Lives