Learn from acquaintances, and you are clever; from friends, and you are intelligent; from enemies, and you are shrewd; but learn from all, and you are wise.
A shrewd enemy will teach you more than a foolish friend.
It is better to help an enemy than to harm a friend.
Ignore those who resent you. Avoid those who begrudge you. Excuse those who envy you. Pity those who hate you.