On Thursday, Sept. 26, Paul Simon strode into Elisabeth Luce Moore Hall a bit after 3:35, with a casual, “Hi guys, sorry I’m late” to a group of 60 music students. At that moment, this short, balding man in a long-sleeved t-shirt, black jeans, and a baseball cap seemed too ordinary to be legendary. Yet, his voice was unmistakable, and he spoke about songwriting and his life with an air of both thoughtfulness and vast experience.