Fig. 1.

Three categories of social dilemmas and their utility functions. (A) Threshold problems (such as overfishing) possess a threshold structure where utility is high at small values of $n$, is low at high values of $n$, and decreases exclusively within an intermediate range. (B) Littering, on the other hand, is an aggregation problem, where each piece of litter adds the same negative utility to the outcome, and thus there is no delimited threshold range. (C) Another class of problems, coordination problems, have a high expected utility if everyone either decides to take the action or not take the action (such as driving on the left side of the road).