Most of us believe we are rational decision makers. But medical decisions are especially complex, thanks to the numerous unknowns and the uniqueness of each person's body. Suppose you've just found out that you or a loved one has prostate cancer, one of the many examples in Jerome Groopman and Pamela Hartzband's illuminating new book, "Your Medical Mind." Nearly every urologist would recommend radical surgery to remove the organ. Sounds reasonable, doesn't it? But let's look at the numbers more closely. Prostate cancer is slow-moving; more people die with it than from it. According to one 2004 study, for every 48 prostate surgeries performed, only one patient benefits—the other 47 patients would have lived just as long without surgery.