Letters 31.5

Work is the sustenance of noble minds. There is, then, no reason why, in accordance with that old vow of your parents, you should pick and choose what fortune you wish should fall to your lot, or what you should pray for; besides, it is base for a man who has already travelled the whole round of highest honours to be still importuning the gods. What need is there of vows? Make yourself happy through your own efforts; you can do this, if once you comprehend that whatever is blended with virtue is good, and that whatever is joined to vice is bad. Just as nothing gleams if it has no light blended with it, and nothing is black unless it contains darkness or draws to itself something of dimness, and as nothing is hot without the aid of fire, and nothing cold without air; so it is the association of virtue and vice that makes things honourable or base.

Seneca, Letters to Lucilius 31.5, translated by Richard Mott Gummere