It is not things in themselves which trouble us, but our opinions of things.
Whoever does not regard what he has as most ample wealth, is unhappy, though he be master of the world.
To the rational being only the irrational is unendurable, but the rational is endurable.
Seek not good from without; seek it within yourselves, or you will never find it.
Other people's views and troubles can be contagious. Don't sabotage yourself by unwittingly adopting negative, unproductive attitudes through your associations with others.
We have two ears and one mouth so that we can listen twice as much as we speak.