What is the theme in Prisoner's Dilemma by William Poundstone?

Another theme is individual rationality and collective irrationality. Aside from the reality of conflict that game theory can show us, one of the other truly disturbing results is the way individual rationality can subvert individual goals and lead to outcomes that look collectively irrational. In a prisoner's dilemma, both parties would prefer to cooperate, but given the logic of the game, it is rational for each party to defect, leading to an outcome that looks collectively irrational. This is also often true in assurance games or stag hunts as well.