A quote
Now if we are agreed on this point, it is natural that we shall be agreed on the following also—namely, that the happy life depends upon this and this alone: our attainment of perfect reason. For it is naught but this that keeps the soul from being bowed down, that stands its ground against Fortune; whatever the condition of their affairs may be, it keeps men untroubled.
Seneca·Letter 92 (§2)·trans. Gummere