In the same line of thought ...

 It is part of human nature to hate the man you have hurt. (Tacitus)

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Here is what can sometimes happen: one person wrongs another and doesn't know how to come back from that. So they deepen the wrong. They add further or worse misdemeanours, falsehoods, calumnies or what have you to the original one. This is the dynamic: to reinforce the thought that the first wrong wasn't one, anything which might diminish its recipient helps the offending party convince him or herself that the other must be a bad person, so that the first offence against them was somehow deserved. The deepening process is itself the symptom of a moral discomfort that cannot be squarely faced. (Normblog)

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Nicholas frowned. He had done much evil to the Poles. To justify that evil he had to feel certain that all Poles were rascals, and he considered them to be such and hated them in proportion to the evil he had done them. (Normblog)

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... independently of that, she disliked Fanny, because she [i.e. Mrs Norris] had neglected her... (Normblog)

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 “There is perhaps no surer way of infecting ourselves with virulent hatred toward a person than by doing him a grave injustice.”

 “Propaganda ... serves more to justify ourselves than to convince others; and the more reason we have to feel guilty, the more fervent our propaganda.” ― Eric Hoffer, The True Believer: Thoughts on the Nature of Mass Movements