Cicero stated, “There is no duty more indispensable than that of a returning a kindness. All men distrust one forgetful of a benefit.” In his book Man in Reciprocity, Becker (1956) uses this quote to show that men have been insisting on the importance of reciprocity for a long time.<re>Becker, Howard. Man in Reciprocity. New York: Prager, 1956, p.1.</ref> Cialdini (2001), in concordance, states that evolutionary selection pressure has probably entrenched the behavior of reciprocity in most social animals. Social equilibrium and cohesion among humans could not exist without the reciprocity of service and return service. All contact among people rests on the schema of giving and returning the equivalence, according to sociologist Simmel (1950). The above information makes a case for the belief that the norm of reciprocity has been crucial to the evolutionary development of mankind.