In one’s friend one shall have one’s best enemy. Thou shalt be closest unto him with thy heart when thou withstandest him.
 Friedrich Nietzsche, Thus Spoke Zarathustra (1891). copy citation

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Author Friedrich Nietzsche
Source Thus Spoke Zarathustra
Topic heart enemies
Date 1891
Language English
Reference
Note Translated By Thomas Common
Weblink http://www.gutenberg.org/files/1998/1998-h/1998-h.htm

Context

“If one would have a friend, then must one also be willing to wage war for him: and in order to wage war, one must be CAPABLE of being an enemy.
One ought still to honour the enemy in one’s friend. Canst thou go nigh unto thy friend, and not go over to him?
In one’s friend one shall have one’s best enemy. Thou shalt be closest unto him with thy heart when thou withstandest him. Thou wouldst wear no raiment before thy friend? It is in honour of thy friend that thou showest thyself to him as thou art? But he wisheth thee to the devil on that account!
He who maketh no secret of himself shocketh: so much reason have ye to fear nakedness!” source