Terry Goodkind. Wizard's first rule (№ 7152)

Here on Earth, there is neither good nor evil in its purest form. Even the best of people may experience evil thoughts, an honest man is capable of low action. And evil: not in the world of the villain, devoid of a shred of virtue. Not the villain who does evil, Rada about their own welfare. Such a person will always found an excuse. My cat, when hungry, was hunting mice. Does this mean that it is bad? I don't think so, and the cat doesn't think so, but I bet the mouse stick on this account a somewhat different opinion. Every killer believes that their actions are necessary and justified.
It's all in the perception. It is always the winner no doubt of the correctness, and the loser is sure that he had been treated unfairly.