The tragedy of the Commons is when there is a public good that, if most people contribute, everyone gets back more than they put in, but because it's rational f

The tragedy of the Commons is when there is a public good that, if most people contribute, everyone gets back more than they put in, but because it's rational for each person independently to not contribute (since it isn't strictly necessary for them in particular), it fails to happen. You know, like not contributing your Union dues.