If not, in a few words: A common resource is overused until it fails, thus imperiling everyone who is using it. In other words, each user of the commons optimizes for themselves, ignoring the the larger consequences and advantages, until there is a total system failure.
The usual example given is a number of farmers grazing their cattle on a common pasture until the pasture fails entirely and endangers everyone's livestock.
In a posting entitled "The Tragedy of the Risk Perception Commons" Matthew Squair explains a behaviorial risk that is related:
A person, perceiving a risk, as a member of a group affected by the risk, has an obligation to speak up and direct attention to risk assessment and mitigation. But, if in doing so, the person is cast down by the group's members and made unwelcome or unproductive in the group, then the person faces the optimization dilemma in full force:
- Optimize on a personal level and withdraw the challenge to the group to address the risk, thereby re-establishing themselves with the group; or
- Sub-optimize on a personal level (in trade for optimizing on the larger level) by continuing to challenge the group to address the risk
However, game theory, which I've talked about before, is a tool for just this situation. Two parties, seeming uncollaborative and even hostile in some scenarios, more or less muddle through with a suboptimum solution because they can't bring themselves to do better by joining their collective skills and reasoning.
In Game Theory 101, this is similar to the classic "prisoner's dilemma". The prisoners couldn't figure it out, and we aren't likely to do that much better unless everyone understands the tragedy of the commons.