My introductory quote for this article comes from a medical magazine, written by a doctor. The subject matter, The Lancet outcome study of patients treated at the Bristol Cancer Centre, is probably now only of historic interest. The quote, however, is pithy, eloquent, inspiring and flawed. Doctors almost invariably think that what they are doing is right for the patient or they wouldn’t be doing it. Mental health professionals, who are perhaps more reflective than some doctors, usually believe they are right as well. Most health-care professionals are well-meaning people who believe they do their best and that what they do is reasonably successful. They couldn’t work otherwise. And usually they are right, because most illnesses, especially the ones we see in psychiatry, tend to improve. If not, they at least wax and wane, to give the illusion of improvement—like depression or asthma. From the patients’ perspective, providing they meet a doctor or therapist who is nice, courteous and respectful, things are normally not too bad. Most patients report good outcomes because they may have got better anyway, and because they like their doctor or therapist. And, finally, all treatments seem to work better in acute single illnesses, as opposed to chronic, complex conditions occurring in patients with other multiple risk factors and disadvantages, so it is not surprising that we prefer to give our best treatments to those who seem most likely to benefit. So how, then, can a doctor decide what really does work, and how can a patient know whether or not the treatment that the doctor recommends with such conviction stands a better than even chance of making him or her better? The answer is via the randomized controlled trial (RCT).