It’s tough to say which single Stoic principle has helped me the most in the time I’ve been engaged with Stoicism in a more than casual manner. Stoicism is, after all, a systematic philosophical perspective, where the principles don’t work to anything like their full potential in isolation. There’s also the difficulty of trying to recall and weigh against each other the myriad times I’ve in one manner or another used, recalled, or relied upon a Stoic principle.
So it is with a bit of reluctance that I zero in on one of them in particular, a reticence that stems not from the usefulness, and perhaps even necessity of that principle for myself and likely for others, but rather from a concern with truthfulness about and fidelity to my experience. That said, what principle is it?
It’s not one derived directly from one single passage from classic Stoic texts, though it does tie into a number of them. It’s this: with each choice or prioritization, each action or emotional response on your part, you are doing something that matters with the manifold of your habits. Put more simply: each time, you’re making yourself better or worse as a person, within the lasting but also changeable core of who you are.
Epictetus, who identifies this “what you are” as prohairesis, the “faculty of choice” (3.1) also stresses at many points that we need to attend closely to our habits, and be ready to put in the work to change them from worse to better.
Virtues and vices, main aspects of our moral character for Stoics, are not (as some mistakenly believe) only types of knowledge (epistēmai) , but are identified also as habits or dispositions (hexeis, diatheseis) at multiple points in Stoic texts. That should be rather unsurprising, given that nearly all ancient schools of virtue ethics held some similar views. What’s particularly important here for this principle is that, when we are in real-life situations, where we choose, prioritize, act, or feel, what we do must be understood as feeding into our habits in one way or another, and as bearing upon our character, the virtues or vices we possess or are possessed by.
It is not as if by simply doing one thing wrong we fall immediately from virtue into vice. Nor can we similarly transform ourselves from vicious to virtuous just by choosing one uncharacteristic good action. We should think of moral aspects of our character as cumulative results at any given time of what we have previously accustomed ourselves to. So the principle that every moment, every choice, every action does matter to our moral formation or degeneration, even when it seems a small or trivial thing, is a reminder that many of us need.
We might be tempted to say, when we do something that is in some small way making us worse off, that it’s really not a big deal. Epictetus recalls a time when he said something like that to his teacher Musonius Rufus. “It’s just a mistake in a syllogism. It’s not like I burned down the capitol” (1.7) . Rufus responds (paraphrased): “Buddy, that mistake you made? In this that is burning down the capitol.”
Another common way of fooling ourselves is, while admitting that what we’re doing is the wrong thing, we justify it just in this particular case. We make an exception for ourselves, just this one time (it won’t be the only time!), or in these unusual circumstances, or because right now I’m pressed for time, or have a lot on my plate, or. . . Pick whatever reason you like, it doesn’t change the fact that when we give in like that we strengthen a habit we ought to be working to root out.
Sometimes we recognize habit’s cumulative force, but we mistakenly think we can balance matters out. Sure, I’m giving in to anger right now, but next time around, I’ll react differently, and that will make up for this time. Doubtful! How are you going to be any better the next time you start to feel anger? You just strengthened one already bad habit, and perhaps a second one, precisely that of making that sort of excuse.
As someone who has struggled with the vice of irascibility, I’ve certainly benefitted from this principle of treating every instance as the moment that genuinely matters for my moral character. Quite likely applying it would pay off well for you as well.
This piece first appeared in the May 2026 issue of the online magazine The Stoic. If this piece has you now interested in Stoicism, and you would like to know what to read next, this might be helpful for you.
Gregory Sadler is the founder of ReasonIO, the co-founder of The Stoic Heart®, a speaker, writer, and producer of popular YouTube videos on philosophy. He is co-host of the radio show Wisdom for Life, and producer of the Sadler’s Lectures podcast. You can request short personalized videos at his Cameo page. If you’d like to take online classes with him, check out the Study With Sadler Academy.
I would agree with you in choosing this principle as one of the most personally helpful in applying Stoicism (or ancient virtue ethics in general) to life. Not only does it provide another incentive to act virtuously, even when the consequences are minor, but it also seems to be true. I'm no neuroscientist, but my lay understanding is that we do indeed reinforce a particular neural network every time we engage in a certain sequence of thoughts, feelings, and actions. Every time we make a particular excuse for an unvirtuous act and follow it up with action, we reinforce that neural pathway. Every time we choose something different, we reinforce a different pathway.
The principle of focusing on the virtuousness of each small action in the moment also relieves the anxiety that comes from trying to imagine all the consequences of every possible choice, estimate their likelihood and choose the best one.
For me personally, I think the MOST impactful principle is eudaimonism - the idea that virtue is the surest path to happiness/flourishing. I know it more from Aristotle than from the Stoics. I haven't encountered as much discussion of eudaimonia in my study of the Stoics so far. If there are particular texts that discuss the idea in depth, I would love some recommendations!