So why do we get angry when our enemies hurt us? Because we didn't expect that particular injury, or at least not something so bad. This happens because we love ourselves too much. We think we should stay safe even from our enemies. Everyone carries the heart of a tyrant inside them — we're happy to dish it out, but we don't want to take it. So anger comes from either ignorance or arrogance. Ignorance of basic facts. What's so surprising about bad people doing bad things? What's new about your enemy hurting you, your friend fighting with you, your son screwing up, or your servant making mistakes?
How is it, then, asks our opponent, that we are angered by the injuries inflicted by our enemies? It is because we did not expect those particular injuries, or, at any rate, not on so extensive a scale. This is caused by our excessive self-love: we think that we ought to remain uninjured even by our enemies: every man bears within his breast the mind of a despot, and is willing to commit excesses, but unwilling to submit to them. Thus it is either ignorance or arrogance that makes us angry: ignorance of common facts; for what is there to wonder at in bad men committing evil deeds? what novelty is there in your enemy hurting you, your friend quarrelling with you, your son going wrong, or your servant doing amiss?