Q.What is the 'Tragedy of the Commons'? Why are common-pool resources especially prone to environmental degradation?

Resources nobody individually owns face a very particular incentive problem that privately-owned resources do not.

The Tragedy of the Commons describes what happens to a common-pool resource — a resource such as open grazing land, a common fishery, or a shared groundwater aquifer, which is not owned by any single individual and can be freely accessed by many users.

The underlying problem is an incentive mismatch: any individual user who extracts a bit more of the resource (grazes one more animal, catches a few more fish) gains the entire private benefit of that extra use for themselves. But the cost of that extra use — a slightly more depleted pasture or fishery for everyone — is shared among all users, so each individual bears only a small fraction of the cost their own extra use creates. Since every user faces this same incentive, each one is led to keep using more, even though the cumulative effect of everyone doing so overexploits and eventually depletes the resource for all of them — an outcome that leaves everyone worse off than if usage had been limited and coordinated. …

Confusing the Tragedy of the Commons with a simple externality — the key distinguishing feature here is the ABSENCE of ownership over a shared r …