We have all known years of continued favors forgotten, and their memory wiped out by one small failure to grant a new request for help.

We have all known malignant hate to be the return for long periods of lavish kindness.
Ingratitude is robbery.

It robs those to whom gratitude is due, for it is the withholding of that which is justly theirs.

If you are kind to another, is he not your debtor?
If you show another favors, does not he owe you thanks?
True, you ask no return, for love does not work for wages.

Only selfishness demands repayment for help given, and is embittered by ingratitude.