Letters from a Stoic
You should be extending your stay among writers whose genius is unquestionable, deriving constant nourishment from them if you wish to gain anything from your reading that will find a lasting place in your mind. To be everywhere is to be nowhere. People who spend their whole life travelling abroad end up having plenty of places where they can find hospitality but no real friendships. The same must needs be the case with people who never set about acquiring an intimate acquaintanceship with any one great writer, but skip from one to another, paying flying visits to them all.
Each day, too, acquire something which will help you to face poverty, or death, and other ills as well. After running over a lot of different thoughts, pick out one to be digested thoroughly that day.
According to Epicurus, ‘A cheerful poverty is an honourable state.’ But if it is cheerful it is not poverty at all. It is not the man who has too little who is poor, but the one who hankers after more.
You warned me to avoid discussing your affairs freely with your friend, since you are not even in the habit of doing so yourself; in other words you have described him as being a friend and then denied this, in one and the same letter... if you are looking on anyone as a friend when you do not trust him as you trust yourself, you are making a grave mistake.
Think for a long time whether or not you should admit a given person to your friendship. But when you have decided to do so, welcome him heart and soul, and speak as unreservedly with him as you would with yourself.
Refrain from following the example of those whose craving is for attention, not their own improvement, by doing certain things which are calculated to give rise to comment on your appearance or way of living generally. Avoid shabby attire, long hair, an unkempt beard, an outspoken dislike of silverware, sleeping on the ground and all other misguided means to self-advertisement... Inwardly everything should be different but our outward face should conform with the crowd. Our clothes should not be gaudy, yet they should not be dowdy either. We should not keep silver plate with inlays of solid gold, but at the same time we should not imagine that doing without gold and silver is proof that we are leading the simple life.
Note: Seneca's advice reminds me of Sam Harris's idea of spiritual materialism – pretending to be above others by being "more spiritual".