The degree of enthusiasm for prostate cancer screening seems high given the limited evidence of benefit and the well-documented harms of treatment that include impotence and incontinence. The purpose of this review is to understand the reasons for enthusiasm and positive reinforcement perceived in clinical decisions about whether to screen, whether to choose aggressive therapy for cancer, and in how to view adverse effects following therapy. We discuss a case of a man who must decide whether to undergo prostate-specific antigen screening and treatment to illustrate the kinds of reinforcement that may occur for each decision.Strong positive reinforcement for each decision would make screening and aggressive therapy appear to be successful and the correct decision even if prostate cancer screening and therapy were not beneficial. A physician is positively reinforced for recommending screening, regardless of the test result, because a negative result makes a patient grateful for reassurance and a positive result makes a patient grateful for early detection. A patient who is impotent and incontinent after a decision for curative treatment may attribute his survival to surgery and be grateful for having his cancer cured. Individual experience provides almost no negative feedback that early detection and aggressive treatment may not work. Although reinforcement operates similarly in other medical decisions, the example of prostate cancer provides insight into the strength of the forces at work because the personal harms, which are relatively common and dramatic, are readily discounted or explained away. Even if prostate cancer screening is eventually demonstrated to provide benefit for asymptomatic persons, it is important to appreciate the strength of forces that may act independently of benefit and reinforce decision makers' choices to be aggressive about screening and treatment. Interventions should be considered to temper possible overenthusiasm for screening and treatment.