Is it Simply Mind Over Matter?
In the Marine Corps, we used to have a saying, “If you don’t mind, it doesn’t matter.” I often found that to be true – both there and in long distance adventure racing – that I could actually keep going, even when every muscle in my body said STOP. The same thing is true for CrossFitters. Check out this article from the NY Times about training your mind in all sorts of ways:
100 Burpee Pull Ups for time.