The evolution of drug resistant microbes is one of the key challenges for 21st century medicine. Drug use practices vigorously advocated as resistance management tools by professional bodies, public health agencies and medical schools represent humankind’s largest attempts to manage evolution. Yet some of these practices seem to sit uncomfortably with ecological and evolutionary principles, or at the very least, seem overly simplistic. I will illustrate this by examining the advice that patients should keep taking their antibiotics even when they feel better. Intuition is unreliable even in simple evolutionary contexts; developing a science of resistant management requires that evolution be measured.