E. Issues frequently become political when private and social costs differ. F. Moreover, once a decision is political, it almost inevitably implies costs and benefits for people who opposed the decision, not just its supporters. The Tragedy of the Commons A. Economists usually focus on how ownership gives people incentives to use resources in a sensible way. But it is possible for something to be unowned. This has frequently happened.
Oceans are normally unowned, accessible to all.
Since no one owns it, people use it without regard to the effect on others. And, once you realize that people think this way, you also have an incentive to take as much as possible NOW, because the resource won't be useful very long. That is the benefit of property rights that is absent in the commons - a benefit not just for owners, but for users as well. In sum, the basic idea of the tragedy of the commons is that when no one owns a resource, it gets over-used. It means that there are costly side effects that selfish agents don't factor into their decisions.