This article presents a critical examination of the general weight that modern deterrence theory assigns to cost–benefit rationality in its conception of criminal acting out. Following Niklas Luhmann and Spencer Brown, who state that observation means handling distinctions, we reveal what the distinctions in deterrence theory themselves conceal, in particular with respect to these “other rationalities” (that is, rationalities other than rationality defined in terms of cost–benefit calculation), which may, in certain circumstances, have a significant influence on the decision-making process involved in acting out. In empirical terms, based on excerpts from qualitative interviews we conducted with individuals who had committed “serious” crimes, we support this hypothesis by showing the operating procedure for an alternative defined in terms of the rationality of risk. In relation to criminal law, our analysis therefore challenges an entire set of assumptions dear to deterrence advocates; in relation to science, it reopens a now-stagnant debate regarding the criteria for the effectiveness or operationalization of criminal deterrence.