Mean, median and mode - three ways to statistically look at "the middle." It is in this vein that Seneca teaches us to not be too radical in our way of life on either end of the spectrum. In Aristotelian philosophy, the idea would be called the Golden Mean.
In this letter, Seneca advocates for a life of temperance, by avoiding extremes and excesses. More precisely, he advocates for the self-improvement of the philosopher and not for self-aggrandizement.
I commend you and rejoice in the fact that you are persistent in your studies, and that, putting all else aside, you make it each day your endeavour to become a better man. I do not merely exhort you to keep at it; I actually beg you to do so. I warn you, however, not to act after the fashion of those who desire to be conspicuous rather than to improve, by doing things which will rouse comment as regards your dress or general way of living.The right course of action for a philosopher is to work on the inward - the inner dialogue - and to focus less on the outward appearance. And for outward appearances, the philosopher ought to maintain good decorum. He writes:
Inwardly, we ought to be different in all respects, but our exterior should conform to society ... Let us try to maintain a higher standard of life than that of the multitude, but not a contrary standard; otherwise, we shall frighten away and repel the very persons whom we are trying to improve.Because Stoics believe in and practice social oikeiosis, they want to try to influence fellow citizens for the better. But if they (the Stoics) are too radical in appearance or demeanor, then their influence for good would be less effective. Seneca tried to strike the right balance with this thought:
Philosophy calls for plain living, but not for penance; and we may perfectly well be plain and neat at the same time. This is the mean of which I approve; our life should observe a happy medium between the ways of a sage and the ways of the world at large; all men should admire it, but they should understand it also.