The sucker effect is a type of group motivation loss or social loafing effectan instance in which a person works less hard as a member of group than as a comparable individual performer. The sucker effect occurs when people perceive that they are doing more than their fair share of the group's work; one way to reduce the injustice of such a situation is to reduce their own level of effort.

For example, suppose you are working on a three-person lab project in your chemistry course. Suppose that you see that you are doing much more of the work on the project than your two lab partners. If everyone in the group receives the same grade based on the quality of the final lab report, your ...