In the standard rational choice model, actors have exogenously given beliefs that perfectly match objective probabilities. As such, these beliefs cannot be optimistic or motivated by preferences, even though substantial empirical evidence indicates that human beliefs routinely satisfy neither of these criteria. I present a tractable Endogenous Beliefs Model and apply it to three different political environments from across the subfields of political science. In the model, players form beliefs that maximize a utility function that represents preferences over outcomes and the anticipatory experience of uncertainty. Applications include voter turnout, taxation and collective choice, and crisis bargaining. The model captures the empirical evidence about belief formation much better than the standard model. Moreover, these applications show how rigidly insisting on the standard rational choice model rejects otherwise reasonable explanations by fiat, precisely because of its implausible assumptions about beliefs.