This is the first of a series of four articles on psychological foundations from an applied psychological perspective. To begin with, the psychology of give and take, which is contradictory in its application, like many basic psychological mechanisms: sometimes emphasized, sometimes denied. In this first article it is argued that humans are equipped with a psychological reciprocity mechanism that constantly judges whether give and take in the social group we belong to is in balance (reciprocal altruism: favour others at their own expense, because it is later repaid). On the other hand, sometimes it is necessary to hide inequalities in give and take, especially in a complex hierarchical society.