The Theory of Moral Sentiments by Adam Smith

There is another set of passions, which, though derived from the imagination, yet before we can enter into them, or regard them as graceful or becoming, must always be brought down to a pitch much lower than that to which undisciplined nature would raise them. These are, hatred and resentment, with all their different modifications. With regard to all such passions, our sympathy is divided between the person who feels them, and the person who is the object of them. The interests of these two are directly opposite. What our sympathy with the person who feels them would prompt us to wish for, our fellow-feeling with the other would lead us to fear. As they are both men, we are concerned for both, and our fear for what the one may suffer, damps our resentment for what the other has suffered. Our sympathy, therefore, with the man who has received the provocation, necessarily falls short of the passion which naturally animates him, not only upon account of those general causes which render all sympathetic passions inferior to the original ones, but upon account of that particular cause which is peculiar to itself, our opposite sympathy with another person. Before resentment, therefore, can become graceful and agreeable, it must be more humbled and brought down below that pitch to which it would naturally rise, than almost any other passion.

Mankind, at the same time, have a very strong sense of the injuries that are done to another. The villain, in a tragedy or romance, is as much the object of our indignation, as the hero is that of our sympathy and affection. We detest Iago as much as we esteem Othello; and delight as much in the punishment of the one, as we are grieved at the distress of the other. But though mankind have so strong a fellow-feeling with the injuries that are done to their brethren, they do not always resent them the more that the sufferer appears to resent them. Upon most occasions, the greater his patience, his mildness, his humanity, provided it does not appear that he wants spirit, or that fear was the motive of his forbearance, the higher the resentment against the person who injured him. The amiableness of the character exasperates their sense of the atrocity of the injury.