Meditations, Book 4, Section 37

Marcus Aurelius — The Emperor

Always remember what Heraclitus said: earth dies and becomes water, water dies and becomes air, air dies and becomes fire, and so on in reverse. Also remember the person who didn't know where the path led. Think about this: reason governs everything in the world. People deal with it constantly and intimately. Yet it's the very thing they fight against most. The things that happen to them every day keep seeming strange to them. We shouldn't speak or act like people who are sleepwalking, driven by opinions and fantasies. When we do that, we only think we're speaking and acting. And we shouldn't be like children who just copy their parents, giving no better reason than "this is how we learned it" or "this is what our ancestors passed down to us."

Marcus Aurelius — The Emperor Original

Let that of Heraclitus never be out of thy mind, that the death of earth, is water, and the death of water, is air; and the death of air, is fire; and so on the contrary. Remember him also who was ignorant whither the way did lead, and how that reason being the thing by which all things in the world are administered, and which men are continually and most inwardly conversant with: yet is the thing, which ordinarily they are most in opposition with, and how those things which daily happen among them, cease not daily to be strange unto them, and that we should not either speak, or do anything as men in their sleep, by opinion and bare imagination: for then we think we speak and do, and that we must not be as children, who follow their father's example; for best reason alleging their bare καθότι παρειλήφαμεν; or, as by successive tradition from our forefathers we have received it.