Why does Marcus Aurelius say a man should not compete praise, power or pleasure with virtue?

Marcus is not making a claim about willpower or discipline. He is making a claim about what actually belongs to you. In Meditations 3.6, he says that if you find anything better than justice, truth, temperance, and fortitude, anything better than your own mind's self-satisfaction in acting according to right reason, then you should turn to it with your whole soul. That is a genuine offer, not a rhetorical trap. But he immediately narrows the field: if nothing surpasses "the deity which is planted in you," the rational faculty that governs your impressions and appetites, then nothing else should be allowed to compete with it, including "praise from the many, or power, or enjoyment of pleasure" (Meditations 3.6).

The common misreading treats this as advice to ignore reputation and comfort because they are distracting or beneath a serious person, a kind of stoic austerity for its own sake. That reading turns the passage into a lifestyle preference. Marcus is making a sharper and stranger claim: praise, power and pleasure are not just lesser goods, they are not goods at all in the sense that matters. Elsewhere in the Meditations he gives the reasoning behind this. Honour and dishonour, pain and pleasure, "all these things equally happen to good men and bad, being things which make us neither better nor worse. Therefore they are neither good nor evil" (Meditations 2.11). A thing that falls on the just and the unjust alike, without tracking their character at all, cannot be what makes a life good. Only the rational faculty, the part of you that judges, chooses, and directs your impulses, is entirely up to you. Everything else, including whether people applaud you or whether you hold office or whether the pleasure you feel is intense, depends partly on the world.

This is why Marcus frames praise, power and pleasure as things that could come into competition with virtue at all. They can imitate the good. A promotion feels like proof you did well. Applause feels like confirmation. Pleasure feels like the thing life is for. Marcus warns that these things, even when they seem to align with the better good in some small way, can obtain the superiority all at once and carry a person away (Meditations 3.6). The danger is not that they are obviously bad. It is that they are close enough to good to hijack your attention if you let them enter the comparison at all.

What changes for someone who takes this seriously is the standard by which they judge a day well spent. You stop asking whether people noticed, whether you gained influence, or whether the experience felt good, and you start asking whether your judgments were sound and your actions followed reason. Marcus even anticipates the objection that would restore praise or pleasure to the contest: someone will say that what is useful is what is better. His answer is to ask what kind of usefulness you mean. If it is useful to you as a rational being, keep to it. If it is only useful to you as an animal, say so plainly, and examine the claim by a sure method rather than assuming it settles anything (Meditations 3.6).

The practical move is small and repeatable. Before you chase an outcome, whether it is a compliment, a promotion, or a pleasure, ask which faculty in you it serves. If the answer is your capacity to judge and act well, pursue it without hesitation. If the answer is only appetite or vanity, you are free to still want it, but do not mistake it for the good, and do not let it outbid the thing that is actually yours to keep.