The joint exploitation of open-access natural resources is often modeled as a social dilemma with no escape for rational actors. Nevertheless, real individuals are not helplessly trapped in this dilemma and are often able to sustainably manage their commons by building endogenous institutions. This paper proposes both a simple analytical model and a more complex agent-based one designed to study common-pool resource management problems with a specific focus on the relation between agents’ beliefs and institutions. The conditions where agents are allowed to build management institutions lead to much better outcomes than the ones where agents can only rely on individual beliefs in order to limit the resource consumption. This happens despite the fact that agents act in a competitive environment favoring high resource consumers.