Price theory is made richer by the fact that each individual’s choices can affect the opportunities available to others. If you decide to eat all of the cake, your roommate cannot decide to eat some too. An equilibrium is an outcome in which each person’s behavior is compatible with the restrictions imposed by everybody else’s behavior. In many situations, it is possible to say both that there is only one possible equilibrium and that there are good reasons to expect that equilibrium to actually come about. This enables the economist to make predictions about the world
