Conjunction Fallacy

Conjunction fallacy is a source of behavioral bias in decision making. The term basically refers to the tendency to believe that a combination of events is more likely than any of the events on their own. For example, people tend to overweight the probability of an early death because they can imagine (and overweight) the possibility of many different sources of the early demise. In contrast, longevity risk is relatively difficult to imagine and break-down into separate events. As a result, longevity risk is often underweighted.