Another one that really seems to resonate with me more as I get older.

"People change so you can learn to let go" 

Sometimes that person is you. You change, and sometimes that means letting go of certain things. Even certain people.

"Things go wrong so you can appreciate them when they're right"

Whether it's appreciating them when they finally come back around, or whether it's appreciating the new thing when it comes along. But just learning to appreciate what you have, and not to so easily let go of a good thing. 

Good things are rare now a days.