Meditations 4.24

Occupy thyself with few things, says the philosopher, if thou wouldst be tranquil.—But consider if it would not be better to say, Do what is necessary, and whatever the reason of the animal which is naturally social requires, and as it requires. For this brings not only the tranquillity which comes from doing well, but also that which comes from doing few things. For the greatest part of what we say and do being unnecessary, if a man takes this away, he will have more leisure and less uneasiness. Accordingly, on every occasion a man should ask himself, Is this one of the unnecessary things? Now a man should take away not only unnecessary acts, but also unnecessary thoughts, for thus superfluous acts will not follow after.

Marcus Aurelius, Meditations 4.24, translated by George Long

If thou wouldest be tranquil in heart, says the Sage, do not many things. Is not this a better maxim: do but what is needful, and what the reason of a living creature born for a civic life demands, and as it demands. For this brings the tranquillity which comes of doing few things no less than of doing them well. For nine tenths of our words and deeds being unnecessary, if a man retrench there, he will have more abundant leisure and fret the less. Wherefore forget not on every occasion to ask thyself, Is this one of the unnecessary things? But we must retrench not only actions but thoughts which are unnecessary, for then neither will distracting actions follow.

Marcus Aurelius, Meditations 4.24, translated by C. R. Haines