It is always easier to requite an injury than a service: gratitude is a burden, but revenge is found to pay.

Revenge is profitable, gratitude is expensive

Revenge is a much more punctual paymaster than gratitude

Gratitude is a burden, and every burden is made to be shaken off

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

Revenge is profitable, gratitude is expensive.