For those who hold the opinion that things are good or bad by nature are perpetually troubled. When they lack what they believe to be good, they take themselves to be persecuted by natural evils and they pursue what (so they think) is good. And when they have acquired these things, they experience more troubles; for they are elated beyond reason and measure, and in fear of change they do anything so as not to lose what they believe to be good. But those who make no determination about what is good or bad by nature neither avoid nor pursue anything with intensity; and hence they are tranquil.
Sextus Empiricus, Outlines of Scepticism. Translated by Annas and Barnes.