In a slightly more detailed picture, here are the quotes I live by:
"Just because it is, doesn't mean it should be." (Australia, the movie)
I like to challenge certain habit, customs, conventions because I don't think they should exist.
"Shoot for the stars because if you miss, you'll land on the moon." (not sure who said this)
I believe that until we exhaust ourselves trying, we can't know how much we can accomplish.
"Treat others the way you want to be treated."
Don't take this too literally though because what's right for you may not be right for everyone, but I always make efforts to find what the other person wants and give them that. Of course, that also means that if I treat someone kindly, I expect the same kindness in return; I don't aspire to be a saint.
I prefer truth over tact. I think tact generally hinder problem solving: can't fix what you don't see. However, being truthful doesn't mean being hurtful, and I always try to limit my truth to what is necessary (my mouth do get away from me sometimes).