I like to read quotes about optimism, and here are a few that I found:

“A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty.” 
― Winston Churchill

“What day is it?"
It's today," squeaked Piglet.
My favorite day," said Pooh.” 
― A.A. Milne

“Man often becomes what he believes himself to be. If I keep on saying to myself that I cannot do a certain thing, it is possible that I may end by really becoming incapable of doing it. On the contrary, if I have the belief that I can do it, I shall surely acquire the capacity to do it even if I may not have it at the beginning.” 
― Mahatma Gandhi