From Arrian the pupil of Epictetus.
To the man who was bothering himself about the problem of being
1What do I care, says Epictetus, whether all existing things are composed of atoms, or of indivisibles, or of fire and earth? Is it not enough to learn the true nature of the good and the evil, and the limits of the desires and aversions, and also of the choices and refusals, and, by employing these as rules, to order the affairs of our life, and dismiss the things that are beyond us? It may very well be that these latter are not to be comprehended by the human mind, and even if one assume that they are perfectly comprehensible, well, what profit comes from comprehending them? And ought we not to say that those men trouble themselves in vain who assign all this as necessary to the philosopher's system of thought? Is, therefore, also the precept at Delphi superfluous, "Know thyself"?—That, indeed, no, the man answers.—What, then, does it mean? If one bade a singer in a chorus to "know himself," would he not heed the order by paying attention both to his fellows in the chorus and to singing in harmony with them?—Yes.—And so in the case of a sailor? or a soldier? Does it seem to you, tlien, that man has been made a creature to live all alone by himself, or for society?—For society.—By whom?—By Nature.—What Nature is, and how she administers the universe, and whether she really exists or not, these are questions about which there is no need to go on to bother ourselves.
Source: Stobaeus, Eclogue, II. 1, 31