I've posted this before, but here they are also relevant:
F. Scott Fitzgerald : "Never confuse a single defeat with a final defeat."
and
Success is sweet and sweeter if long delayed and gotten through many struggles and defeats." -Amos Bronson Alcott

I love it too! I used to work at a residential group home for adolescent girls, and we used to put a quote up on the chalk board in the kitchen every day. That was always my favourite, and used it quite a few times!