An important part of the legal system is the system of property rights. Property rights are rules governing the use and disposition of resources. Private property rights embody incentives that lead to the efficient use of resources. Individuals who use their resources inefficient bear the costs of the inefficiency in the form of lower incomes. Common property rights embody an entirely different set of incentives.
Common property entails a nonexclusive right to use a resource.
The notion of rationality implies that resources are used up to the point where the marginal benefit of their use equals the marginal cost. The problem with common property is that, so far as the individual is concerned, there is no cost to using the common resource. If you do not use it, someone else may and it will not be available for your use. Individuals do not consider the alternative uses of common property resources and thus view them as being free. The consequences of these perverse incentives are the overutilization of resources.