
“That which is good for the enemy harms you, and that which is good for you harms the enemy.”
Quello che giova al nimico nuoce a te, e quel che giova a te nuoce al nimico.
Rule 1 from Machiavelli's Lord Fabrizio Colonna: libro settimo (Book 7) http://babel.hathitrust.org/cgi/pt?id=njp.32101013672561;view=1up;seq=176 (Modern Italian uses nemico instead of nimico.)
The Art of War (1520)