Four laboratory studies show that people are more likely to accept others' unethical behavior when ethical degradation occurs slowly rather than in one abrupt shift. In the studies, participants served in the role of watchdogs charged with catching cheating in a series of trials. The cheating they observed increased either gradually or abruptly; people were more likely to overlook cheating that increased gradually. Our studies also provide evidence as to why people accept cheating by others. Our results indicate that the effect is due at least in part to the failure to notice that unethical behavior is occurring when the change is gradual rather than abrupt.