How tiny a fragment of boundless and abyssal time has been appointed to each man! For very swiftly is it swallowed up in the eternal. And how tiny a part of universal substance! How tiny a clod of the all-embracing earth! And how tiny a portion of all things is the present, on which alone thou crawlest! Reflecting on all this, consider nothing great save this: to act as thy nature leads, and to bear what the common nature brings.
Two clauses worth slowing down on. Act as thy nature leads — for the Stoics, human nature is rational and social. So to act according to nature is to act with reason and with regard for the common good. Bear what the common nature brings — accept what the larger order delivers, even when it costs. The fragment is short; spend it on these two things.
Marcus Aurelius, Meditations 12.32 · trans. Modernized (translator unverified — not Long; see audit notes) (2000s)
Context
One of the last passages of the Meditations — Marcus Aurelius near the end of his own life, returning to a theme he never tired of. The brevity of human life is not a reason to despair. It is a reason to be precise about what to spend it on.