Josie King’s senseless death started with a hot bath. The one-and-a-half-year-old girl climbed into a tub and burned herself in January 2001. Her initial recovery, at a large hospital, seemed promising, but then the toddler began experiencing insatiable thirst. Nurses told her mother not to let her drink and said that her vital signs were normal, even as she sucked washcloths to quench her thirst. Then, despite a no-narcotics order, a nurse gave Josie methadone, which led to cardiac arrest. Two days later, she died in the intensive-care unit.

Josie’s mother, Sorrel, told this heartbreaking story in December 2004 at an event kicking off a campaign to reduce by 100,000 the number of patients who die each year in US hospitals because of preventable errors.¹ A small nonprofit called the Institute for Healthcare Improvement (IHI) was behind the 100,000 Lives campaign. By June 2006, the hospitals enrolled in it had accomplished this goal.² Although the organization lacked formal authority over the hospitals and operated with a tiny staff and modest resources, it helped save 100,000 lives by inspiring and guiding executives, physicians, nurses, and a host of other staff members in the 3,000 hospitals (representing over 75 percent...