I need some motivational quotes by well known sports figures?

I want a quote to put in a card – something along the lines of "you’ve done great so far, but the real test is still ahead" – and I’d like it to be by a sports figure because the recipient of the card is all about sports- but I dont know a first down from second base, so I have no idea who I might want to look up.

I used Jimmy V’s famous speech (espy awards) last year.
What should I try now?

Thanks all

"Just Do It"-NIKE