What did Marcus Aurelius say about controlling your mind?

In Meditations Book 8, section 47, Marcus Aurelius writes: “If you are pained by any external thing, it is not this thing that disturbs you, but your own judgment about it. And it is in your power to wipe out this judgment now.” Writing as Roman emperor, privately, for himself rather than for publication, Marcus is applying a core Stoic claim first developed by Epictetus (whose Enchiridion opens with the same distinction between what is “up to us” and what is not): events themselves are indifferent, and it is the mind's verdict on those events — this is bad, this is unbearable, this should not be happening — that produces suffering, not the event in its own right. The same passage continues by widening the point beyond momentary pain: if what distresses you is something in your own character, nothing stops you from correcting your principles right now either, since character too is a matter of judgment rather than fixed fate. This is not a claim that external events don't matter or can be wished away — Marcus elsewhere acknowledges real hardship, illness, and loss throughout Meditations — but a claim about where the actual site of suffering is located: not in the world, which simply happens, but in the running commentary the mind adds to it. Because that commentary is a judgment, and judgments are formed by the person making them, Marcus treats it as revisable in the moment, which is why he frames the fix as something available “now” rather than as a distant goal to work toward.