Medical overuse, or health services for which potential harms outweigh benefits, is common and persistent. Medical overuse is assumed to exist when regional variation occurs without improvements in outcomes and is believed to be driven largely by perverse financial incentives and local cultures of care.1 In this issue of JAMA Internal Medicine, Schwartz and colleagues2 quantified variations in primary care physician provision of low-value services (largely representing overuse) among Medicare beneficiaries and characterized associations with physician characteristics such as age, training, and research activities. Although practice varied widely within organizations, little variation was due to observable physician characteristics. These findings suggest that overuse drivers go beyond incentives and culture and that reducing overuse will require deeper understanding of physician behavior.