"Sometimes I sit and think about every stupid thing I've ever done." (it is a horrible feeling!) :P (this picture/quote comes to mind quite frequently for me.
Louisa May Alcott "Little Women" Not Afraid of Storms Quote
A little wisdom from Calvin + Hobbes "If people sat outside and looked at the stars each night, I'll bet they'd live a lot differently. When you look into infinity, you realize that there are more important things than what people do all day.