Meditations 6.19

If a thing is difficult to be accomplished by thyself, do not think that it is impossible for man: but if anything is possible for man and conformable to his nature, think that this can be attained by thyself too.

Marcus Aurelius, Meditations 6.19, translated by George Long

Because thou findest a thing difficult for thyself to accomplish do not conceive it to be impracticable for others; but whatever is possible for a man and in keeping with his nature consider also attainable by thyself.

Marcus Aurelius, Meditations 6.19, translated by C. R. Haines