Margen
The most powerful man of his time wrote notes to scold himself. That is what Marcus Aurelius's Meditations are: a private journal, written in Greek between military campaigns, that its author never meant to publish.
That's why rereading it works: there's no pose. Here is an emperor reminding himself that he must get out of bed, that it isn't worth arguing with fools, that fame is smoke others breathe. His most useful technique is still the morning preparation: at waking, anticipate that today you'll cross paths with selfish, impatient and ungrateful people, so that it neither surprises you nor governs you.
The underlying lesson hasn't expired in eighteen centuries: power over others is a lottery; power over oneself is a craft. And it's practised in writing.