The tragedy of the commons is a concept that was popularized in a 1968 article
by Garrett Hardin.
He wrote about a patch of unregulated land - a “commons” - where farmers bring their herds to graze. If one of the farmers decides to add an extra animal to their herd they will benefit. However if all the farmers were to do the same thing, the land will become overgrazed and depleted, and everyone will suffer the loss of the shared resource - the commons. As Hardin puts it:
Therein is the tragedy. Each man is locked into a system that compels him to increase his herd without limit-in a world that is limited. Ruin is the destination toward which all men rush, each pursuing his own best interest in a society that believes in the freedom of the commons.