Book VI · 22
I do my duty: other things trouble me not; for they are either things without life, or things without reason, or things that have rambled and know not the way.
I do my own duty; other things do not distract me. For they are either inanimate or irrational, or such as have gone astray and know not the road.
Marcus Aurelius, Meditations VI.22. Translated by George Long (1862). The Stoic Library.