Medicine has been identified as a profession for almost 3000 years based on a core premise that physicians have the right to evaluate their own quality. Because medicine is a profession and because of the special privileges granted to physicians by society, quality-based principles that evolved in the manufacturing business have been difficult to adapt to medical practice. Physicians learn from other physicians and medical literature. This leads to wide variation in what is considered best practice. Variation has complex association, including the variation in expert opinion, the complexity of medical knowledge, the variation in physician decision-making potential, and human error. Guidelines or algorithms are a strategy that are finding favor as a solution. The control of variation through guideline development, iterative refinement of guidelines, and feedback to physicians will improve medical practice. By removing variation, physicians can honor the fiduciary trust that they have made to patients, make reasoned decisions, improve outcomes, and focus attention on making medical improvements.