Right before you head out running, it can be hard to remember exactly why you're doing it. You often have to override a nagging sense of futility, lacing up your shoes, telling yourself that no matter how unlikely it seems right now, after you finish you will be glad you went. It's only afterward that it makes sense, although even then it's hard to rationalize why. You just feel right. After a run, you feel at one with the world, as though some unspecified, innate need has been fulfilled.