Patients don't always know when their doctor has made a medical error. But other doctors do. A few years ago I called a Las Vegas surgeon because I had hospital data showing which of his peers had high rates of surgical injuries – things like removing a healthy kidney, accidentally puncturing a young girl's aorta during an appendectomy and mistakenly removing part of a woman's pancreas. I wanted to see if he could help me investigate what happened. But the surgeon surprised me. Before I could get a question out, he started rattling off the names of surgeons he considered the worst in town.