3.20.1
In the case of appearances which are objects of the vision, nearly all have allowed the good and the evil to be in ourselves, and not in externals. No one gives the name of good to the fact that it is day, nor bad to the fact that it is night, nor the name of the greatest evil to the opinion that three are four. But what do men say? They say that knowledge is good, and that error is bad; so that even in respect to falsehood itself there is a good result, the knowledge that it is falsehood. So it ought to be in life also. Is health a good thing, and is sickness a bad thing? No, man. But what is it? To be healthy, and healthy in a right way, is good to be healthy in a bad way is bad; so that it is possible to gain advantage even from sickness, I declare. For is it not possible to gain advantage even from death, and is it not possible to gain advantage from mutilation? Do you think that Menoeceus gained little by death? Could a man who says so, gain so much as Menoeceus gained? Come, man, did he not maintain the character of being a lover of his country, a man of great mind, faithful, generous? And if he had continued to live, would he not have lost all these things? would he not have gained the opposite? would he not have gained the name of coward, ignoble, a hater of his country, a man who feared death? Well, do you think that he gained little by dying? I suppose not. But did the father of Admetus gain much by prolonging his life so ignobly and miserably? Did he not die afterwards? Cease, I adjure you by the gods, to admire material things. Cease to make yourselves slaves, first of things, then on account of things slaves of those who are able to give them or take them away.