The paper presents the model of human relations based on the generalization of the utility function, which accounts for the existence of the intrinsic motivation resulting from
reciprocity, and of the crowding-out effect. The model is used to reanalyze the problem of the investment in a public good, where positive, but less-than-Pareto-optimal investment is now possible in equilibrium, which corresponds to the experiment’s results in this domain. Under certain conditions even equilibrium of equal distribution of incomes among group members is now possible, but this equilibrium becomes fragile when the group size increases.