What matter and opportunity [for thy activity] art thou avoiding? For what else are all these things, except exercises for the reason, when it has viewed carefully and by examination into their nature the things which happen in life? Persevere then until thou shalt have made these things thy own, as the stomach which is strengthened makes all things its own, as the blazing fire makes flame and brightness out of everything that is thrown into it.

X, 31 - Meditations (c. 161–180 CE) - Book X