What did Marcus Aurelius say about self-discipline?

Self-discipline was not, for me, a matter of harsh repression — it was the very foundation of a life worth living. The soul that cannot govern itself is governed by something lesser: appetite, fear, the opinions of others. In the Meditations, I recorded what I learned from those around me about this practice of inner governance. From my grandfather Verus I took lessons in gentleness and the restraint of anger; from my mother, as I wrote in the First Book, I learned “to content myself with a spare diet, and to fly all such excess as is incidental to great wealth”. These were not mere rules imposed from outside — they were habits cultivated so that virtue would be ready when circumstances demanded it. The deeper point is this: every thought shapes what you will become. As I observed in the Meditations, “Such as thy thoughts and ordinary cogitations are,' he says, 'such will thy mind be in time”. This is why I drilled my soul in right principles — not waiting for the emergency to decide how to act, but preparing long beforehand. Self-discipline, rightly understood, is simply the act of keeping the rational and governing part of oneself in its proper place — ruling the passions, not enslaved to them. That is the whole of it.