Heuristics - Availability
If examples are readily available in our memory, then we presume that other such examples are commonplace. Do more people live in Iraq or Tanzania? Most likely answer to how readily Iraqis and Tanzanians come to mind. Most people, having vivid images of Iraqis, guess wrong. Although, we are often well served by this cognitive rule, called the availability heuristic. The more easily we recall something, the more likely it seems.