We propose a new theoretical approach that offers a parsimonious motivational explanation for human cooperation. In order to cooperate people have to agree on how to structure their interactions. Despite individual differences in important social motivations, people usually succeed in coordinating with each other in a wide variety of social settings. We suggest that the state of a relationship in which social actors apply the same relational schema to structure their interaction (Relational Complementarity) is intrinsically motivating, no matter what its content is. Relational schemas are conceptualized according to Relational Models Theory that suggests only four universal models that are used to structure all human interactions: Communal Sharing, Authority Ranking, Equality Matching and Market Pricing. Because relational schemas enable the understanding, anticipation, planning and generation of action, the application of the same schema by interacting actors allows them to congruently complete each other’s actions and to interact with fluidity and smoothness, as opposed to the awkwardness, misunderstanding and conflict that characterize non complementary states. Relational Complementarity provides people with a temporary sense of connection through cognition and action that is not experienced if each applies a different schema. We claim that Relational Complementarity potentially addresses a wide variety of fundamental human motives to comply with situational demands and social expectations that have been suggested by several theories, because while complementing each other people experience a sense of understanding (each other’s intentions), belonging (to a relationship), control (over own and other’s actions), and trust (on each other’s intentions), amongst others.

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