People should either be caressed or crushed. If you do them minor damage they will get their revenge; but if you cripple them there is nothing they can do. If you need to injure someone, do it in such a way that you do not have to fear their vengeance.

Niccolò Machiavelli

There are minds so impatient of inferiority that their gratitude is a species of revenge, and they return benefits, not because recompense is a pleasure, but because obligation is a pain

Samuel Johnson