Social interaction occurs in various ways through daily life and different social roles. There are several common forms of social interaction, including exchange, where people interact with the expectation of receiving something in return; reciprocity, the idea that favors deserve repayment; and exchange theory where people are motivated by self-interest. Other forms are competition between groups for limited resources, conflict which involves attempts to harm others, and accommodation which balances cooperation and conflict through compromise or truce. Cooperation also occurs when groups work together to achieve mutual benefits.