A defining element of catastrophes is the magnitude of their harmful consequences. To help society prevent or mitigate damage from catastrophes, immense effort and technological sophistication are often employed to assess and communicate the size and scope of potential or actual losses. This effort assumes that people can understand the resulting numbers and act on them appropriately.

However, recent behavioural research casts doubt on this fundamental assumption. Many people do not understand large numbers. Indeed, large numbers have been found to lack meaning and to be underweighted in decisions unless they convey affect (feeling). As a result, there is a paradox that rational models of decision-making fail to represent. On the one hand, we respond strongly to aid a single individual in need. On the other hand, we often fail to prevent mass tragedies – such as genocide – or take appropriate measures to reduce potential losses from natural disasters. This might seem irrational but we think this occurs, in part, because as numbers get larger and larger, we become insensitive; numbers fail to trigger the emotion or feeling necessary to motivate action.