Many words have been spoken by Plato, Zeno, Chrysippus, Posidonius, and by a whole host of equally excellent Stoics. I’ll tell you how people can prove their words to be their own—by putting into practice what they’ve been preaching.
—Seneca, Moral Letters, 108.35; 38
One of the criticisms of Stoicism by modern translators and teachers is the amount of repetition. Marcus Aurelius, for example, has been dismissed by academics as not being original because his writing resembles that of others, earlier Stoics. This criticism misses the point.
Even before Marcus’s time, Seneca was well aware that there was a lot of borrowing and overlap among the philosophers. That’s because real philosophers weren’t concerned with authorship, only what worked. More important, they believed that what was said mattered less than what was done.
And this is as true now as it was then. You’re welcome to take all of the words of the great philosophers and use them to your own liking (they’re dead; they don’t mind). Feel free to tweak and edit and improve as you like. Adapt them to the real conditions of the real world. The way to prove that you truly understand what you speak and write, that you truly are original, is to put them into practice. Speak them with your actions more than anything else.
* Source: The Daily Stoic by Ryan Holiday and Stephen Hanselman