Some of these may already be posted, forgive me if they have been.
Whether you think you can or think you cant, you're right-Henry Ford
A wise man can learn more from a foolish question than a fool can learn from a wise answer-Bruce Lee
If you can't explain it simply, you don't understand it well enough-Albert Einstein
That last one may be miss quoted but that's the basic idea.
I really like all three of these especially the AE quote, someone had it as their signature in an email years ago and it just made a lot of since to me.
Surprisingly Bruce Lee has some really good ones out there, he seemed to be ahead of his time and who knew he was more than just kick butt kung fu movies. hahaa