When we learn about a severe moral transgression that has been committed, we are often not only horrified but also puzzled. We are inclined to raise questions such as ‘Why did they do this?’ or exclaim: ‘I cannot understand why anyone would do such a thing!’. This suggests that there is something difficult to understand about severe moral wrongs. In this paper, I offer an explanation of the phenomenon that severe moral transgressions are often difficult to understand. I begin by (...) arguing that the relevant sense in which we try but often fail to understand morally bad action is that we try but fail to empathize with the agent at the time of the action. Then, I introduce a distinction between two broad kinds of morally bad action. Finally, I show that each of these kinds of morally bad action gives rise to obstacles to empathizing with the agent at the time of the action. Based on this explanation, I consider whether we should try to overcome this limitation to our understanding. (shrink)