In 2012, Paul Kibbett checked into a California hospital to have his cancerous right kidney removed. Surgeons erroneously took out his left kidney instead. After his doctors went back to remove the diseased kidney, Kibbett had to rely on dialysis for the rest of his life. The next year, a Pennsylvania man with chronic pain in his right testicle awoke from surgery to learn that the doctor had mistakenly removed his left testicle.

Such devastating errors, known as wrong-site surgeries, happen because the protocols meant to prevent them are counterintuitive and too often ignored. And doctors and hospitals are not required to report such accidents, which makes the problem harder to study. Some estimates suggest that wrong-site surgery happens about once in every 100,000 surgeries, which would mean hundreds of times per year in the United States. Some experts believe that as few as 10 percent of these mistakes are ever reported, so the accidents we know about may be the tip of the iceberg. But regardless of how common they are, these botched procedures are profoundly damaging. They are also more preventable than experts recognize.