Nash equilibrium: a situation where any party would be worse off if they altered their strategy. To prevent cheaters from ruining the successful collaboration of a large group, it may be in everyone’s interest to relinquish some power to a higher level in the hierarchy that can punish cheaters: for example, people may collectively benefit from granting a government power to enforce laws, and cells in your body may collectively benefit from giving a police force (immune system) the power to kill any cell that acts too uncooperatively (say by spewing out viruses or turning cancerous).
