Cicero said you should never believe something for which you don’t have what the philosophers call ‘sufficient epistemic warrant.’ The Stoics argued that if you want to live a good life, you need to understand the world in which you live as much as possible. Because if you don’t understand it, or if you misunderstand it, then you’re going to make bad decisions, some of which may be fatal.

So, in other words, you have to practice science, as we would say today — not as a professional scientist, of course — but you have to have a minimum understanding of how the world works.