The standard belief-desire account of the explanation of action is inadequate to the task of explaining even the very simplest actions. We must suppose instead that three psychological states are in play when we explain action, not just two: desire, belief, and the exercise of the capacity to be instrumentally rational. Once we enrich our understanding of action explanation to acknowledge the causal role played by an agent’s exercise of his rational capacities, much richer accounts of action explanation come into view, accounts that highlight the many different ways in which agents’ actions can be explained by their rational capacities. Of special interest are cases in which agents’ actions are explained by their failure to exercise their rational capacities, where these are capacities that they possess, and cases in which their actions are explained by their failure to exercise their rational capacities, where these are capacities that they do not possess. Richer accounts of action explanation such as these suggest a distinctive story about the conditions under which people are responsible for wrongdoing, a story with surprising implications for our understanding of what it is for an agent’s moral beliefs to be justified.