S.J.
Pursuit of Happyness - that movie is probably the most inspirational I have watched.
The part where the dad (will smith) and the son are playing basketball and the little boy is telling his dad he wants to be a basketball player when he grows up. Will Smith then basically tells him to be realistic and not get his hopes up. After a few minutes, Will realizes what he has done, grabs the boy, gets on his level and basically says "listen to me boy, don't you EVER let anyone tell you you can't do something, not even me". It is great!
I am sure there are other parts of this movie you could use - this one just stands out in my mind.
I sure hope your movie clip isn't the same one, I cannot watch youtube at work!!
Good luck - what a fun question!