My little sister is going to rehab for two years, I'm going to send her a postcard everyday with an inspirational quote to help her, what is your favorite inspirational quote?

My little sister has a terrible addiction and will be checking into Rehab on Wednesday. She won't be able to talk to or see anyone for 90 days but she can get letters. I want to send her a postcard everday with a motivational quote that will help her.

What quotes have really stuck in your mind that have helped you or others in your lives?