"An agent who regarded [sound moral principles] as mere rules of thumb would ignore them whenever she calculated that compliance wasn’t necessary to minimize the cumulative badness of suffering. The problem is that it might also be in her own interest to violate these principles, and self-interest could distort her calculations, even when she calculated sincerely. She could thus acquire a pattern of violating the principles even when compliance with them really was necessary to prevent the worst cumulative suffering. To avoid this, we would want her to feel strongly inhibited from violating the principles. Inhibitions of this kind can insulate agents from the effect of biased calculations."