The needles go under the skin, into a layer of fat. Three times per week, for over a decade, Shirley had taken one of the pre-filled syringes from her refrigerator and injected her thighs. Then I met her.

Doctors had given her a diagnosis of multiple sclerosis years earlier. The word crippled her. She’d stopped driving, stopped working, and adjusted to the stigma of having a chronic disease. She didn’t like shots, but “that’s life,” she said. She hadn’t had a flare since her initial diagnosis, and she was grateful for the time she’d enjoyed with grandchildren and great-grandchildren. I talked to her about her symptoms, encouraged her to stop smoking, and ordered more of the medication she’d been taking.

I saw her a second time five months later, after she suffered a rare reaction — anaphylaxis — from the medication I’d renewed. She had been admitted to the hospital, where another doctor had reviewed her history. She’d had an unusually benign course for someone with longstanding disease. The white spots on her brain scan, which we had thought were from multiple sclerosis, were probably from high blood pressure, high cholesterol or diabetes. Shirley might not have had multiple sclerosis at all.

Medical school teaches us to examine, to research, to treat. We don’t learn to err and recover. Nobody stands behind a podium and declares: “Each of you will make mistakes, and some of them will hurt people.” We don’t consider the unavoidable tension between human fallibility and the responsibility to care for people’s lives.