Abstract in UndeterminedThe aim was to use Todd Ebert's Hats puzzle to devise a Dutch Book showing that individual rationality could add up to collective irrationality even if the players aim to promote common goals. Situations in which this happens involve violations of what might be called the Group-Reflection Principle. The Dutch book that can be set up against groups that violate Group-Reflection is a version of van Fraassen’s Dutch book against individual agents who violate the standard individual version of Reflection.Unfortunately, as it turned out, the argument leading to the paradox is flawed, but it is flawed in interesting ways. It was based on the betting interpretation of the subjective probabilities, but ignored the fact that this interpretation does not take into account the strategic, i.e. game-theoretic, considerations that might influence an agent’s betting behavior. If such considerations are taken into account, as they clearly should, then the Dutch book construction crumbles.Thus, the argument that individual rationality in pursuing a common objective can add up to collective irrationality does not go through after all. Instead, the lesson to be learned concerns the interpretation of probabilities in terms of fair bets and, more generally, the role of game-theoretic considerations in epistemic contexts. Another lesson concerns Group-Reflection, which in its unrestricted form is a highly counter-intuitive principle. We consider how this principle of social epistemology should be formulated so as to make it tenable.