How do we keep improving as human beings? By adopting a buddy system of course! Plenty of modern research does show that a very effective way to stick by our commitments is to partner up with a friend (or even a mobile app!), who will keep tabs on us and help us carry on with whatever pursuit we decided to engage in. If the help is reciprocal, all the better.
In a sense, the entirety of Seneca's famous letters to his friend Lucilius may be understood as just one such buddy system, where the more expert Seneca is guiding his younger friend, though the quest for becoming better people is shared, and the help is reciprocal.
Letter 36 actually begins with Seneca advising Lucilius to, in turn, give some comfort to another friend, supporting him in his decision to abandon a position of prestige in order to pursue a life of reflection:
Prosperity is a restless thing; it drives itself to distraction. It addles the brain, and not always in the same way, for it goads people in different directions -- some toward power, others toward self-indulgence. (36.1)
Power and pleasure, for Seneca, are distractions from the real task: moral self-improvement. They are "preferred indifferents," of course, meaning that they have some value, in that they do make our life more comfortable. But too much of them, and now we mistake instrumental goods for intrinsic ones, the ends for the means.
Now is the time to learn. 'What do you mean? Is there any time that isn't the time to learn?' Not at all: it is honorable to learn at every time of life, but by the same token there is a time at which it is not honorable to be tacking the introductory course. (36.4)
I love the subtle sarcasm seeping through here. Yes, of course, as the common saying goes, it's always a good thing to learn something new, regardless of one's age or stage in life. But, Seneca suggests exploiting the school analogy, we really ought to get started on the early side of things, so that we are not caught by old age still learning the basics.
Fortune has no jurisdiction over his conduct. Let him take charge of that himself, so that his mind may achieve its perfection in complete tranquility, not perceiving any loss or any gain, but retaining the same attitude no matter what befalls. If commonplace goods are piled around him, he towers over his possessions; if chance knocks down one of the piles, or all of them, he does not thereby become shorter. (36.6)
Seneca is now talking again about Lucilius' friend, using his example to make a fundamental point: luck certainly plays a role in our lives, as it influences externals, such as our access to material goods, or the people we meet and interact with. But it does not control our own judgments and intentions to act. In that sense, the wise person is free from the vagaries of fortune, so long as he maintains an attitude of equanimity toward both gains and losses. Do we benefit from a sudden stroke of good luck? Very well, let us enjoy it, but not to the point of becoming cocky and assuming that it was deserved, or that the universe could never take it back. Do we, by contrast, experience a setback? Very well, let us not catastrophize about it, reminding ourselves that others have suffered through similar situations and have pulled through. We can certainly do the same, if we put our mind to it. But what if what we face is what Seneca elsewhere calls the ultimate test of our character, death itself?
No one doubts that there is something frightening about death, something jarring not only to the body but to our rational nature, which has been designed for self-love. There would be no need to sharpen ourselves up in preparation for something that we were inclined to pursue willingly and instinctively in the same way that all creatures have a drive for self-preservation. (36.8)
Here Seneca is -- as usual -- being very pragmatic and commonsensical. No lofty talk of the silliness of being afraid of death. Of course death is frightening, more so precisely because we are capable of reflecting on what it means, the annihilation of our self. But it is that very same capacity for reason that is going to help us put things into perspective, realize that death is a natural and inevitable phenomenon, and even that it is precisely its very approaching -- at any time -- that makes our life meaningful and our decisions relevant.
Another day I will give you a fuller explanation of how all things that seem to perish are in fact transformed. He who departs with the expectation of returning ought to depart calmly. Consider cycles in the natural world: you will see nothing that is actually extinguished: rather, things descend and rise again by turns. (36.11).
Concluding his letter, Seneca refers to the famous doctrine of the pre-Socratic philosopher Heraclitus of Ephesus, "panta rhei," everything flows. Heraclitus said that we never step into the same river twice, because it is never the same river. This approach is actually now a dominant view in modern philosophy, referred to as "process metaphysics" (as opposed to "object metaphysics," where the focus is on objects, not on processes). As astronomer Carl Sagan famously put it, we literally come from stardust, and we are constantly recycled in the unfolding of cosmic processes. The Stoics did not believe in the survival of the soul, and were materialists. So there is no comfort here to be taken from the fanciful notion that "we" as individual selves / consciousnesses will continue to exist after death. Seneca is very clear on that in other writings. But our ability to understand both death itself and our connections to the universe at large is what makes us human, and ultimately what allows us to cope with whatever the universe throws at us.