What does Marcus Aurelius mean by saying wrongdoers act through ignorance?

Marcus is not saying wrongdoers are innocent, or that what they do does not matter. He is making a claim about why they do it. In Meditations 2.1, he tells himself to expect, before the day even starts, that he will meet the busy-body, the ungrateful, the arrogant, the deceitful, the envious, the unsociable. His diagnosis is precise: "All these things happen to them by reason of their ignorance of what is good and evil."

The common misreading treats this as a kind of excuse-making, as if Marcus is saying people who wrong us do not really know better and so cannot be blamed at all. That is not the claim. The Stoics held that virtue is a form of knowledge and vice is a form of error. A person acts badly because they have misjudged what is actually good for them. They think status, advantage, or getting one over on someone is good, when in Stoic terms only virtue is good and only vice is bad. Everything else, health, reputation, other people's opinions, is an indifferent, and mistaking an indifferent for a genuine good is exactly the ignorance Marcus has in view.

What follows from this diagnosis is not resignation but a specific kind of clarity. Marcus continues: he has seen the nature of the good, that it is beautiful, and the nature of the bad, that it is ugly, and the nature of the wrongdoer, that it is akin to him, sharing "the same intelligence and the same portion of the divinity." Because of that kinship, he concludes, "I can neither be injured by any of them... nor can I be angry with my kinsman, nor hate him." The reasoning has a structure: people are made for cooperation, "like feet, like hands, like eyelids," and acting against one another is acting against nature.

Notice what Marcus does not say. He does not say the busy-body's rudeness or the deceiver's lie causes him no harm because it feels fine, or because he has trained himself to shrug it off. He says it cannot injure him because nothing external, including another person's bad judgment, can touch what actually makes him good or bad, which is his own faculty of choice. That is the same move Marcus makes elsewhere in Book 2, where he argues that whatever "does not make a man worse" cannot make his life worse either, since good and evil do not fall indiscriminately on people the way pain, pleasure, honor, and dishonor do (Meditations 2.11). The wrongdoer's error is real and it is theirs. It is not automatically transferred into an injury against you.

This reframes anger. If someone's rudeness comes from a mistaken judgment about what is good, then getting angry at them for it is a bit like getting angry at someone for a bad eye that misjudges color. You would not be angry at the eye. You might still name the error, correct it if you can, or protect yourself from its effects. But the anger, the sense of personal injury, drops out, because you no longer think the other person's confusion has the power to make you worse.

The practical use is in the exercise itself. Marcus does this every morning, before he has met anyone. He rehearses the kinds of people he is likely to encounter and reminds himself in advance why their behavior should not surprise him and should not provoke him. The concrete version for you: before a meeting, a family gathering, or a difficult conversation, name in advance the specific ignorance you expect, not to excuse it, but so that when it shows up, you meet it as an error to be worked with rather than an injury to take personally.