The following is an excerpt from What I Talk About When I Talk About Running by Haruki Murakami:
Once, I was lying around a hotel room in Paris reading the International Herald Tribune when I came across a special article on the marathon. There were interviews with several famous marathon runners, and they were asked what special mantra goes through their head to keep themselves pumped during a race. An interesting question, I thought. I was impressed by all the different things these runners think about as they run 26.2 miles. It just goes to show how grueling an event a marathon really is. If you don’t keep repeating a mantra of some sort to yourself, you’ll never survive.
One runner told of a mantra his older brother, also a runner, had taught him which he’s pondered ever since he began running. Here it is: Pain is inevitable. Suffering is optional. Say you’re running and you start to think, Man this hurts, I can’t take it anymore. The hurt part is an unavoidable reality, but whether or not you can stand any more is up to the runner himself. This pretty much sums up the most important aspect of marathon running.