Meditations 5.23

Often think of the rapidity with which things pass by and disappear, both the things which are and the things which are produced. For substance is like a river in a continual flow, and the activities of things are in constant change, and the causes work in infinite varieties; and there is hardly anything which stands still. And consider this which is near to thee, this boundless abyss of the past and of the future in which all things disappear. How then is he not a fool who is puffed up with such things or plagued about them and makes himself miserable? for they vex him only for a time, and a short time.

Marcus Aurelius, Meditations 5.23, translated by George Long

Think often on the swiftness with which the things that exist and that are coming into existence are swept past us and carried out of sight. For all substance is as a river in ceaseless flow, its activities ever changing and its causes subject to countless variations, and scarcely anything stable; and ever beside us is this infinity of the past and yawning abyss of the future, wherein all things are disappearing. Is he not senseless who in such an environment puffs himself up, or is distracted, or frets as over a trouble lasting and far-reaching?

Marcus Aurelius, Meditations 5.23, translated by C. R. Haines