The critique of common knowledge of rationality (CKR) developed in the preceding chapters should convince researchers interested in explaining social reality to simply avoid the concept. The actual cost of abandoning CKR in terms of explaining social behavior is minimal because the Nash equilibrium concept itself is problematic when the recursive nature of interagent beliefs is important and the correlated equilibrium is by far the more cogent equilibrium concept. Nevertheless, it may seem curious that we must reject CKR even in situations where all players are in fact rational. What, after all, is the problem with assuming agents know something that is in fact true? This chapter discusses the pitfalls of naïve epistemic logic, the common knowledge of logicality paradox, the Surprise Examination problem, the modal logic of knowledge, and a solution to the Surprise Examination conundrum.