There's a big difference between someone who can't do something and someone who won't do it. We would forgive many of our slaves if we stopped to think before getting angry with them. But instead, we act on our first impulse. Then, even when we discover we got upset over nothing important, we stay angry anyway. Why? Because we don't want to admit we had no good reason to be mad in the first place. Worst of all, we know our anger is unfair, but that makes us cling to it even harder. We feed it and fan the flames, as if being really furious somehow proves we were right to be angry.
between whether a man cannot or will not do it: we should pardon many slaves, if we began to judge them before we began to be angry with them: as it is, however, we obey our first impulse, and then, although we may prove to have been excited about mere trifles, yet we continue to be angry, lest we should seem to have begun to be angry without cause; and, most unjust of all, the injustice of our anger makes us persist in it all the more; for we nurse it and inflame it, as though to be violently angry proved our anger to be just.