It’s always been a dream of mine to run a marathon, just to be able to brag about it, or to prove to myself that I can do it. There’s no other sporting challenge quite as iconic, and yet most people who complete it are not elite athletes. If other people can do it, I know I can do it, if I set my mind to it. But I’ve never enjoyed running. Even in high school, when cross country was my sport, it was always laborious to me, something I had to do. Afterward, sure, it feels great (and doing...