In 1863, U.S. President Abraham Lincoln wrote a scathing letter to his top Union general, who had squandered a chance to end the Civil War. Then Lincoln folded it up and tucked it away in his desk. He never sent it. Lincoln understood that the first action that comes to mind is often counter-productive. In the third episode of a four-part special series on leadership, HBR Editor in Chief Adi Ignatius and Harvard Business School professor and historian Nancy Koehn explore Lincoln’s career both before and during America’s greatest crisis. They discover lessons on how to learn continuously, communicate values, and exercise emotional self-control.