The guilt left by immoral actions is why moral duties are more pressing and serious than other reasons like prudential considerations. Religions talk of sin and karma; the secular still speak of spots or stains. I argue that a moral staining view of guilt is in fact the best model. It accounts for guilt's reflexive character and for anxious, scrupulous worries about whether one has transgressed. To understand moral staining, I borrow Christine Korsgaard's view that we construct our identities as agents through our actions. The contribution of immoral actions to self-constitution explains why moral obligations have priority and importance.