You will ask, perhaps, what I myself do who preach these things to you. I confess frankly: as is the case with a luxuriant but cautious man, my expense account is balanced. I cannot tell you I lose nothing, but whatever I do lose I can tell you how and why the loss occurred. I can give you the cause of my poverty.
There are 124 extant letters of our stoic philosopher Seneca to his friend Lucilius, admonishing him towards Virtue and warning him against Vice (and at times even reproving him). He instructs him, essentially, on how to become wise man, a sage.
Yet neither Seneca nor any of the other ancient Stoics whose works have been preserved ever claimed to be a wise man. But like anyone who is at least on the correct path towards Wisdom, Seneca is able to discern what he already possesses and what he still lacks. He cannot say he loses nothing, but when he does lose something, he can say how and why. He recognizes his faults, his "poverty", and he is actively remedying them.
But why would Seneca instruct another person on how to live if he has not yet perfected his own advice? Today, if we discover a man's actions are not entirely consistent with his words, we are inclined to label him a hypocrite. But Seneca's is not a case of somebody not practising what he preaches. The Stoic seeks friends whom he can either improve or who can improve him. Lucilius, while having made considerable progress of his own, was still a few paces behind Seneca. Seneca, while not yet perfect himself, was a useful encouragement to his friend. And in helping his friend, he was also furthering his own progress. Elsewhere Seneca famously wrote, qui docet discit, or "he who teaches learns". Just as, for example, a modern day Latin teacher keeps sharp his own knowledge of that ancient language by teaching others, the philosopher rehearses for himself the lessons of his school in the same fashion, training himself as he trains others. (And it is indeed in this spirit that I write these posts; not as one who has already hit the mark, but as one who has made some progress in his aim and needs further practice.) The teacher also becomes accountable to his students in the same way - or even to a greater degree! - as the students are accountable to him. If we ever lose sight of our goal, of Virtue, and have thus momentarily lost that sense of personal shame for our Vices and Passions, perhaps a sense of public shame in the form of the scrutiny of our friends will keep us in check.
We must remember, however, that if we hope to be useful to our friends or they to be any use to us, then we must understand the limits of our successes and "confess frankly" our weaknesses. This requires a substantial amount of personal self-reflection (that is, honesty with one's own self) before one enters into the friendship. My friend cannot help me if he thinks I am flawless; and I do him no good pretending to be so, thereby providing him with a false model to emulate... He will be emulating not a good but a bad man!