For what prevents us from saying that the happy life is to have a mind that is free, lofty, fearless and steadfast – a mind that is placed beyond the reach of fear, beyond the reach of desire, that counts virtue the only good, baseness the only evil, and all else but a worthless mass of things, which come and go without increasing or diminishing the highest good, and neither subtract any part from the happy life nor add any part to it?A man thus grounded must, whether he wills or not, necessarily be attended by constant cheerfulness and a joy that is deep and issues from deep within, since he finds delight in his own resources, and desires no joys greater than his inner joys.
Seneca, The Stoic Philosophy of Seneca: Essays and Letters