Full Idea
If you want a friend, you must be willing to wage war for him: and to wage war, you must be capable of being an enemy.
Gist of Idea
If you want friends, you must be a fighter
Source
Friedrich Nietzsche (Thus Spake Zarathustra [1884], 1.15)
Book Reference
Nietzsche,Friedrich: 'Thus Spake Zarathustra', ed/tr. Hollingdale,R.J. [Penguin 1969], p.82