"Billy had a framed prayer on his office wall which expressed his method for keeping going, even though he was unenthusiastic about living. A lot of patients who saw the prayer on Billy’s wall told him that it helped them to keep going, too. It went like this: “God grant me the serenity to accept the things I cannot change, courage to change the things I can, and wisdom always to tell the difference.” Among the things Billy Pilgrim could not change were the past, the present, and the future."