In letter #3, Seneca discusses the merit and meaning of friendship. He drafts the framework by which a friendship ought to be commenced, perpetuated, or dissolved.
“Deliberate upon all questions with your friend, but first deliberate about him. After friendship there must be full trust, but before it, discretion.
“Trusting everyone and trusting no one are both wrong, though I might say the one wrong is an excess of frankness and the other an excess of security.
“The two attitudes should temper one another: the easygoing man should act, the active man take it easy. Consult Nature: she will tell you that she created both day and night.
*All excerpts have been taken from The Stoic Philosophy of Seneca: Essays and Letters, W.W. Norton.