Even if reason tells us otherwise, the heart...

"It is quite true, we judge men’s character by the way they behave toward us, because they either thought they needed or actually did need to behave in a particular way, whether arbitrarily or by force of circumstance, or indeed intentionally. And if [195] the wickedest person in the world has not done us any harm and for whatever reason has had occasion to help us, even just to treat us well, to be affable, polite, respectful, etc., this will be enough to ensure that we do not think badly of him and even take him for an honest man. Even if reason tells us otherwise, the heart and the imagination will always cling to this conviction. This ought to be the general rule whenever we hear people speaking well or badly of someone. If the person speaking is doing so on behalf of someone else or if he is in bad faith, his motives may be different. But with these two exceptions, normally in your dealings with people you should assume that if someone is telling you about someone else, he has been either well or badly treated by that person, and not expect to learn any more than that from what he is saying. (31 July 1820.)" 

(from "Zibaldone" by Giacomo Leopardi)