Letters 31.6

What then is good? The knowledge of things. What is evil? The lack of knowledge of things. Your wise man, who is also a craftsman, will reject or choose in each case as it suits the occasion; but he does not fear that which he rejects, nor does he admire that which he chooses, if only he has a stout and unconquerable soul. I forbid you to be cast down or depressed. It is not enough if you do not shrink from work; ask for it.

Seneca, Letters to Lucilius 31.6, translated by Richard Mott Gummere