The depletion of a freely accessible resource because a rational individual will base usage decisions on their own self interests even if they know that the cumulative effect of everyone’s actions are depleting the resource. For instance, in the fishing industry each fisherman has an incentive to maximise their own profits by catching as many fishes as possible in the sea, as this is a public resource and does not have clearly defined property rights. However, if each fisherman does this then eventually the sea will become depleted of this type of fish and the industry will suffer.