A blow from your friend is better than a kiss from your enemy.

—Pythagoras

ἀλλήλοις θ᾽ ὁμιλεῖν, ὡς τοὺς μὲν φίλους ἐχθροὺς μὴ ποιῆσαι, τοὺς δ᾽ ἐχθροὺς φίλους ἐργάσασθαι. ἴδιόν τε μηδὲν ἡγεῖσθαι. We ought so to behave to one another as to avoid making enemies of our friends, and at the same time to make friends of our enemies.

—Pythagoras