If you can't run, then walk. And if you can't walk, then crawl. Do what you have to do. Just keep moving forward and never, ever give up.
Dean Karnazes, Ultramarathon Man: Confessions of an All-Night Runner
Never set limits, go after your dreams, don't be afraid to push the boundaries. And laugh a lot - it's good for you!
If you think you can't, you won't, and if you think you can, you will.
Kellie Wells, 2011 USA indoor and outdoor 100m hurdles champion
I don't stop when I'm tired. I only stop when I'm done ...