The paper investigates why justice is regarded as important in human groups and societies. Using the theory of social production functions (SPF) as a general model of action, the theoretical analysis focuses in a first step on the question of why individuals regard justice as valuable in social life. The theory of social production functions defines two fundamental human goals—physical and social well-being. The integration of justice concepts into a general model of human behavior demands to explain how justice enters an individual's social production functions. We predict a direct effect by just procedures that increases social well-being and an indirect effect by stability of auxiliary assumptions given by justice for the production of physical and social well-being. In a second step, the theoretical predictions are tested empirically. The analysis is based on a large dataset that contains 2,926 employees surveyed all over Germany. Using structural equation modeling, the empirical results support our hypotheses: Justice is more important for people who have deficits in physical and social well-being (H1). Moreover, these deficits are more important for justice in the public context than in the private context (H2). It can also be shown that people who work in cooperative situations in which they have to rely on others rate the importance of justice higher (H3). In conclusion, the importance of justice depends on the personal situation and the fulfillment of individual goals, and can be seen as functional on the individual level in ensuring an increase in benefits in cooperative interactions.