Excerpted from A Full Life: Reflections at Ninety by Jimmy Carter. Copyright © 2015 by Jimmy Carter. Reprinted by permission of Simon & Schuster, Inc. All Rights Reserved. INTRODUCTION: Reaching my ninetieth birthday is a good time to look back on moments that changed my life and reflect on some of the memories that are especially important to me. Some of these events affected me profoundly or taught me lessons, large and small. Others are amusing, and some make me contemplate who I was at that time. There are some that I enjoyed and savor, and others that I wish had never happened or that I could change. I spent four of my ninety years in the White House, and they were, of course, the pinnacle of my political life. Those years, though, do not dominate my chain of memories, and there was never an orderly or planned path to get there during my early life. At each step in my career, I made somewhat peremptory decisions about the next one. I had no idea of returning home during...