C. Michael Armstrong, past chairman of the board of trustees of Johns Hopkins Medicine, tells the story of the medical error that sparked his commitment to health care improvement and the creation of the Armstrong Institute for Patient Safety and Quality. In 1993, Mr. Armstrong received a call from the physician who had performed his physical exam during the previous year. The physician explained that Mr. Armstrong’s blood counts had been misread. “I’m so sorry, Mike,” the physician said. “You have leukemia, and we didn’t catch it.” The cancer diagnosis led to Mr. Armstrong undergoing chemotherapy as part of a 30-day clinical trial. He survived not only the cancer, but also a sepsis infection at the end of the trial. Mr. Armstrong’s experiences led him to become a fierce advocate for patient safety and health care quality improvement. In 2011 he announced a $10 million gift to establish the Armstrong Institute, a multidisciplinary group that works to improve health care within Johns Hopkins Medicine and around the world. In 2016, he announced a $5 million gift to establish the institute’s Center for Diagnostic Excellence, the first institute of its kind to take on the challenges of medical misdiagnosis. He and his wife also established the C. Michael and S. Anne Armstrong Professorship in Patient Safety at Johns Hopkins in 2014. Mr. Armstrong is retired chairman of Comcast, AT&T, Hughes Electronics and IBM World Trade Corporation.