On Saturday I watched an annual Easter egg "run and snatch," euphemistically called an Easter egg hunt. The event for 3-to-5 year olds did not go as planned. For some reason, some kids started early. The organizers desperately tried to stop the kids, but it was like standing on the seashore telling the tide to stop rising. (See the results here.) It struck me that the behavior here was very much like the behavior in the problem of the commons, which in turn is a multi-person prisoner's dilemma. It may be desirable for the group as a whole to show restraint, but unless everyone else does, it will harm you to show restraint. Hence, you have no incentive to stop.