The fact that unregulated resources that are held in common are exploited to the point where they lose their usefulness.
Commonly used to argue that having any resources (parks, etc.) held in common will always lead to their destruction. Especially by libertarians and people who want corporate welfare
We could make this publically-owned pristine forest into a public park Governor, but that would only lead to the tragedy of the commons. Let's sell it to the logging intrests instead! Since they'll have ownership over the land, they'll have good reason to take care of it.