The landmark report To Err Is Human was a call to improve the quality of US health care.1 The title refers to a quote from Alexander Pope's An Essay on Criticism (1711): “To err is human, to forgive divine.” The reference is convenient but not entirely appropriate, because forgiveness suggests the commission of sin, which is inextricably linked to fault and blame. A foundation of the patient safety movement is nonjudgmental recognition of the ubiquity of human and system error. By understanding that error—particularly human error—is inevitable but preventable, patient safety efforts focus on improving systems, creating fail-safe mechanisms that intercept error before the bedside, and implementing measures that mitigate harm when an error involves the patient.