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

One of the important themes that come out of this work and out of game theory itself is the reality and ubiquity of conflict. Games like the prisoner's dilemma show that conflicts between people can be very difficult to solve, and in the case of the prisoner's dilemma, it is effectively impossible to solve. We want to think that if only people would think rationally, they would see that cooperation is more beneficial than defection, but the prisoner's dilemma show that it is impossible, in some cases, to rationally demonstrate the value of cooperation.