Seneca and Lucilius shared a friend by the name of Marcellinus, who was going through a bit of a crisis at one point. Who has not been in a similar situation? What are you going to do to help your friend?
Seneca tells Lucilius that Marcellinus doesn’t visit often anymore, a sign of his detachment from his own friends. He is avoiding Seneca in particular because he knows that the philosopher will tell him the hard truth about his situation (about which we don’t actually have any specific detail, unfortunately), and Marcellinus is in no mood to hear the truth.
We see here how much more nuanced the Stoic take is even when compared to that of our close cousins, the Cynics. Seneca is careful, and understands that while Marcellinus needs help, he will not be receptive to a blunt approach, which would probably drive him into further isolation:
Truth should be told only to those who will listen. For that reason, people frequently express doubts about Diogenes and the other Cynics who employed wholesale freedom of speech and admonished everyone they encountered. (XXIX.1)
Nevertheless, if philosophy is to be useful, then this is precisely the sort of circumstances where the rubber hits the road, so to speak. Seneca is still optimistic that he can be of help to his friend, if he extends a hand immediately, but he is also aware that his is, in a sense, a dangerous mission: Marcellinus is strong in character and intellect, and it may be he go ends up dragging his rescuer down, rather than being helped by him.
This is something many of us can relate to. Really helping a friend is a delicate operation, in the course of which we need to steer clear of both the Scylla of being too blunt and thereby closing their mind and the Charybdis of not being sufficiently frank and end up giving vanilla advice that is useless in practice. Moreover, we need to be in a relatively good position ourselves, or we risk falling into the waters from which we were just now attempting to rescue our friend.
Interestingly, Seneca worries that Marcellinus will laugh at the whole notion that philosophy can be of use to him, likely throwing into Seneca’s face a long list of charlatans who fancy themselves philosophers but in reality only sell platitudes. That’s fine, a good Stoic does not mind insults, especially if bearing them is an effective path toward helping someone in need.
Again displaying psychological nuance, Seneca tells Lucilius that in many cases it is simply not achievable to actually cure someone’s spiritual sickness, and all one can aim for is to halt the progression of the disease. Given the circumstances, that still counts as progress. This is true not just for Stoicism, of course, but for any kind of philosophical approach to life’s problems. Philosophy is a powerful tool, but it ain’t no magic wand, and we need to be cognizant of this fact, so that we don’t promise too much to ourselves or others.
Seneca then provides some sound advice to Lucilius, who is in a better position than Marcellinus, and thus more liable to respond well to blunt talk:
While I am getting ready for him, here are my instructions for you. For you have the ability; you understand where you have been and where you are, and infer from that where it is you are headed. Settle your habits; lift your spirits; stand firm against every object of dread; take no account of those who put fear into you. (XXIX.9)
How is one to do this by way of practicing philosophy? The answer to that question is how Seneca ends his letter to his friend, and it is a good reminder for us all:
What, then, will you gain from philosophy. ... Just this: that you would rather please yourself than please the people; that you take thought for the quality, not the number of judgments made about you; that you live without fear of gods or humans; that you either defeat your troubles or put an end to them. (XXIX.12)
Pleasing ourselves rather than others here very clearly should not be intended as an invitation toward selfish indulgence. It is, rather, a reference to the fact that other people’s judgments are not under our control, and that we should therefore focus on improving our own. This is made even more clear by the immediately following clarification that it is important to pay attention to the quality of judgments, not their quantity. If many people with a poor grasp of things criticize you, this counts for nothing compared to the approval and support of a few who do understand how things are. (Remember that, during your next nasty encounter on social media!) Finally, the reference to defeating our troubles or putting an end to them is the recurrent Stoic notion of the “open door”: freedom, as Seneca himself says elsewhere, is only as far as our wrists, but if we decide to keep living, then we have a duty to do our best for ourselves and for the human cosmopolis.