What is the basic premise of the Tragedy of the Commons mentality?

The basic premise of the Tragedy of the Commons is that individuals acting independently and rationally according to their self-interest will ultimately deplete a shared resource, even when it is not in their long-term interest to do so. This occurs because the benefits of exploiting the resource accrue to the individual, while the costs of its depletion are spread across all users. Essentially, the shared resource is "overgrazed" or overused because no single individual has an incentive to conserve it, leading to its eventual ruin for everyone.