Nearly 20 years ago, my brother, Miles, crashed into a tree while skiing too fast down a slick run at Mammoth Mountain, California. I was skiing in front of him, and neither of us were wearing helmets. Ski patrol responded immediately, and Miles was air-lifted to the nearest trauma hospital, where he spent weeks in the intensive care unit. He survived, miraculously, but for the next several years, my brother fought to come back from a traumatic brain injury that altered his life and mine. I always wear a helmet while skiing now. So does he.