When I'm finding it hard to keep going, I count with each step: 1 2 3 4 1 2 3 4. I think I read it in in an article about either the Tour de France or triathlons, and it was for the horrible hill climb bike sections. When you think there's no way you can keep going and you'll never get to the top, even if you can't get all the way, you can surely manage four more steps. And when you've done four, you can do another four etc etc. When I first read it, I was sceptical, but wowee does it work for me!