Tragedy of the commons
Shared resources get overused when each person's incentives diverge from the group's interest.
What it means
The tragedy of the commons is the situation in which individuals, each acting in their own rational self-interest, collectively deplete or degrade a shared, finite resource against everyone's long-term interest. The mechanism is a misalignment of incentives: each user captures the full private benefit of taking one more unit from the commons while the cost of depletion is spread across all users, so the rational individual calculation is to keep taking even as the aggregate of such choices destroys the resource. Hardin used it to argue that unmanaged common resources are doomed without either privatization or top-down regulation. That pessimistic conclusion was substantially qualified by Elinor Ostrom, whose Nobel-winning work documented that real communities around the world have successfully governed commons — fisheries, forests, irrigation systems — for generations through locally evolved norms, monitoring, graduated sanctions, and self-governance, without resorting to either pure markets or external control. The tragedy is therefore a risk, not an inevitability. It matters because it frames many of the gravest collective problems — overfishing, pollution, antibiotic resistance, climate change — while Ostrom's rebuttal points toward institutional solutions beyond the simple market-or-state dichotomy.
Examples
Fishers overfish a common ground until the stock collapses, even though every one of them knew the risk, because each gains from one more catch while all share the loss.
Each person leaves one mug in the office sink because it costs them nothing and the mess falls on everyone — until a washing-up rota and light nagging quietly solve it.
Every doctor who prescribes antibiotics 'just in case' helps one patient today while spending a shared stock of effectiveness that no single prescription noticeably depletes.
First described in Garrett Hardin (1968); Ostrom's rebuttal (1990).