Diogenous Laertiou Peri biōn, dogmatōn kai apophthegmatōn tōn en philosophia eudokimēsantōn biblia 10

...as if nothing were read here that would teach us the duties of a good man (a good man, I say, measured not by the Christian but by the philosophical standard), but because there are other books of others from which these things can be better learned by us. If even the single booklet of Epictetus (whose life I am surprised was prefixed by our Diogenes) would have been a more suitable teacher for us in this matter. But just as the readers of that golden little book are rare, so certainly are those who would rather be better than more learned.

And so much for that preface. I add, moreover, that the title prefixed to this work is so far from deceiving the reader that, on the contrary, these books can be said to hold more in reserve than the front promises, as far as most passages are concerned. For he commemorates many things to us by the way, beyond those about which the title itself promises he will speak. And although in some places he only undertakes to propose the main points of the doctrine of each philosopher (which he calls discussing in headings or by chapters, sometimes adding and elementarily), he nevertheless sometimes provides something more. For we hear him saying in one place, These things are by headings; but in parts, it stands thus.

And let these things said about the work also pertain to its writer; yet those things which will be added below will seem to pertain more properly to the writer himself and to be said about him specifically. First, therefore, it must be noted that it is likely he reports the dogmas of the philosophers faithfully; and as far as the doctrine of Epicurus is concerned, even Cicero himself testifies that he does this for us. For since we read many passages of Epicurean doctrine in his books, we see...