This article questions the view that medical decision-making can be reduced to a series of explicit rules, adherence to which will necessarily improve outcomes. Instead, it attempts to rehabilitate the concepts of clinical expertise and clinical experience, arguing that medicine, like other areas of expertise, depends on forms of implicit knowledge that can only be acquired through years of experience. Recent research on "fast and frugal" heuristics in medical decision-making suggest that statistical techniques are not necessarily superior to clinician judgment. Since clinical decisions are made on individual patients within the constraint of limited information, they must rest on clinical expertise and not clinical rules.