I would have to say "Never give up, never ever give up". That quote is from Paul Hockey, the first one armed Aussie, in the world, to climb Mt. Everest from the north side. I heard a motivational speech from him a few days ago, and that is something I will defiantly be using for a long long time.
Ah, Paul Hockey
After hearing his speech, that quote is probably the one that stuck with me the most. He really made me realise that I can pretty much do anything if I set my mind to it.
"If you know the enemy and know yourself, you need not fear the result of a hundred battles."
-Sun Tzu - The Art of War
My favorite quote:
"Our problems are man-made, therefore they may be solved by man... No problem of human destiny is beyond human beings."
- John "Jack" Fitzgerald Kennedy