vanity fair

"When one man has been under very remarkable obligation to another, with whom he subsequently quarrels, a common sense of decency, as it were, makes of the former a much severer enemy than a mere stranger would be. To account for your own hardheartedness and ingratitude in such a case, you are bound to prove the other party's crime. It is not that you are a selfish, brutal, and angry at the failure of a speculation--no, no-- it is that your partner has led you into it by the basest treachery and with the most sinister motives. From a mere sense of consistency, a persecutor is bound to shew that the fallen man is a villain-- otherwise he the persecutor is a wretch himself."

--W. M. Thackeray, Vanity Fair, chapter XVIII