“ Be like family to your friends, a friend to strangers, and a stranger to your enemies. ”
Additional information: https://twitter.com/naval/status/1312283457930719233
Similar Quotes
Never explain- your friends do not need it and your enemies will not believe you anyway. 
It takes your enemy and your friend, working together, to hurt you to the heart: the one to slander you and the other to get the news to you. 
It's a sad thing not to have friends, but it is even sadder not to have enemies. 
For those who have conquered the mind, the mind is their friend. For those who have failed to do so, the mind acts like an enemy. 
I choose my friends for their good looks, my acquaintances for their good characters, and my enemies for their good intellects. 