Sensitivity theory holds that people differ in both the types of reinforcement they desire and in the amounts of reinforcement they need to satiate. People who crave too much love, too much attention, too much acceptance, too much companionship, or too much of some other fundamental reinforcer are at risk for aberrant behavior because normative behavior does not produce the desired amounts of reinforcement. People who are intolerant of even everyday amounts of anxiety or frustration also are at risk for aberrant behavior. Individual differences in desired amounts of particular reinforcers may predict person-environment interactions, risk factors for psychopathology, and the occurrence of generalized and durable therapy effects versus the occurrence of relapses. Parallel predictions are made for individual differences in tolerance of aversive stimuli. Implications are discussed for applied behavior analysis, the development of psychopathology, and treatment strategies.