The Commons dilemma (tragedy of the Commons) is defined as the depletion or destruction of resources that are owned collectively. It refers to the tendency for shared or jointly-owned resources to be squandered and not used in an optimal or advantageous fashion; a social dilemma in which individuals must decide how much of a shared commodity to use.

The Commons dilemma, also known as the tragedy of the commons, is a psychological and economic concept that describes a situation where individuals, acting in their own self-interest, deplete a shared resource, resulting in a negative outcome for everyone involved.

The term "commons" refers to a resource that is owned or used by a group of people, such as a community park, fishing ground, or pasture land. In such a situation, individuals have a personal incentive to use the resource as much as possible to meet their own needs, but if everyone does so, the resource becomes overused and ultimately depleted.

For example, imagine a small fishing village where there is a communal fishing ground that is accessible to all villagers. Each fisherman wants to catch as many fish as possible to sell at the market, but if everyone fishes too much, the fish population will decrease, making it harder for everyone to catch fish in the future. However, each fisherman may not take into account the impact of their actions on the wider community and instead focus on maximizing their own personal gain.

The Commons dilemma has been studied in psychology, economics, and environmental science, and has important implications for the management of shared resources. Strategies to address the Commons dilemma often involve establishing rules, regulations, or institutions that limit individuals' access to the shared resource, or creating incentives for people to act in ways that benefit the group as a whole.