Meditations 8.36

Do not disturb thyself by thinking of the whole of thy life. Let not thy thoughts at once embrace all the various troubles which thou mayest expect to befall thee: but on every occasion ask thyself, What is there in this which is intolerable and past bearing? for thou wilt be ashamed to confess. In the next place remember that neither the future nor the past pains thee, but only the present. But this is reduced to a very little, if thou only circumscribest it, and chidest thy mind if it is unable to hold out against even this.

Marcus Aurelius, Meditations 8.36, translated by George Long

Let not the mental picture of life as a whole confound thee. Fill not thy thoughts with what and how many ills may conceivably await thee, but in every present case ask thyself: What is there in this experience so crushing, so insupportable? Thou wilt blush to confess. Remind thyself further that it is not the future nor the past but the present always that brings thee its burden. But this is reduced to insignificance if thou isolate it, and take thy mind to task if it cannot hold out against this mere trifle.

Marcus Aurelius, Meditations 8.36, translated by C. R. Haines