The Prisoner’s Dilemma is a problem studied in game theory that shows how two people might not cooperate even if it’s in both their best interests to do so. It highlights the inherent tension between individual interests and a larger society. Should you pick up your trash at the lunch table? Should you push in your chair after getting up? Should you take performance-enhancing drugs? Should you preserve the earth for the next generation? John and Ken find their mutual interests with Cristina Bicchieri from the University of Pennsylvania, author of The Grammar of Society: The Nature and Dynamics of Social Norms.