What makes a patient comfortable or uncomfortable with one treatment or another, or with no treatment at all? Where do these views come from? And how can patients make better decisions? For answers, we spent four years interviewing scores of patients of different ages. We found that a host of powerful and often hidden influences, inside and outside the patient's mind, can sway thinking and distort judgment. We also discovered that, by unmasking those influences, it is possible for patients to gain greater confidence and control over their medical decisions. Many people decline treatment because they know someone who suffered from side effects or someone who lived well into old age without treatment. Stories deeply affect all of us, and they can make real the risks and benefits that might otherwise seem abstract—but they can also distort our vision by making the rare appear routine. Statistics can help to put lessons drawn from stories into a larger context, letting us make a more considered choice than we possibly could by using narratives alone.