Julian has completed five hundred-mile races so far, as well as countless “short” ones, and I once asked him why he does it. He explained it like this: He wants to achieve a completely insular system of accountability, one that doesn’t depend on external feedback. He wants to run a hundred miles when no one knows he’s running, so that the desire to impress people, or the shame of quitting, won’t constitute his sources of motivation. Perhaps this kind of thinking is what got him his PhD at the age of twenty-five. It’s hard to say. Barkley doesn’t offer a pure form of this isolated drive, but it comes pretty close: when it’s midnight and it’s raining and you’re on the steepest hill you’ve ever climbed and you’re bleeding from briars and you’re alone and you’ve been alone for hours, it’s only you around to witness yourself quit or continue.