Here is a strange thing about the man who wrote those words. He was the most powerful person alive, running an empire, and he wrote them to himself in a private notebook he never meant anyone to read.

Marcus Aurelius was a Roman emperor who lived from 121 to 180 CE. And he was not writing advice for the ages. He was reminding himself, on campaign and probably tired, to be good today, because there might not be a tomorrow to be good in.

A quick note before going further. I am not a psychologist or a therapist, and this is one reader’s reflection on an old idea and some modern research, not advice for your life. The studies mentioned here are findings from particular groups of people at particular times, not settled science or rules that apply to everyone. If sitting with mortality brings up something heavier than a passing thought, please don’t carry it alone — a GP, a therapist, or a counsellor is the right person to talk it through with.

The full line, in the George Long translation, reads: “Do not act as if thou wert going to live ten thousand years. Death hangs over thee. While thou livest, while it is in thy power, be good.” That middle sentence usually gets left out, and I understand why. “Death hangs over thee” is a hard thing to put on a mug. But it is the hinge the whole thought swings on.

Most of us treat death as the enemy of a good mood. Don’t think about it, don’t bring it up at dinner, keep it at arm’s length. Marcus does the opposite. He picks it up and holds it close, on purpose, and uses it as a nudge toward better behavior right now.

The trap he names is the ten thousand years. When we quietly assume there is unlimited time ahead, we let the good version of ourselves wait. I’ll be more patient once things calm down. I’ll call my parents more often once I’m less busy. I’ll be the person I mean to be later. Marcus is pointing at that “later” and saying, gently, that it may not arrive. The only reliable place to be good is here, in the time you can actually see.

What I find quietly moving is that he does not phrase it as a grand achievement. Not “change the world,” not “leave a legacy.” Just: be good. While you’re alive. While it’s in your power. It is one of the more doable instructions in all of philosophy, which is probably why it has outlasted the empire he ran.

You might expect science to side with the “don’t think about death” crowd, and for a long time it did. The main theory in this area, called terror management theory, mostly studied the ugly side of thinking about death: the defensiveness, the tribalism, the bad behavior that fear of death can trigger. As psychologist Kenneth Vail put it, this focus became so entrenched that “some have recently suggested that death awareness is simply a bleak force of social destruction.”

Then Vail and his colleagues, in a 2012 review at the University of Missouri, made the case for the other side. Being aware of death, they argued, can also push people toward their health, toward kindness, toward better priorities.

Sound familiar? It is Marcus’s advice, run through a psychology department.

One of their examples is the cemetery study. When people had just been reminded that helping others matters, they helped more near a graveyard than away from one. As Vail reports, helping was “40% greater at the cemetery than a block away from the cemetery.”

The street was the same and the task was the same; the difference was standing near a reminder that we don’t get forever. That is the same direction Marcus was pointing eighteen centuries earlier.

The practical version of Marcus’s line is not morbid. It asks us to look at how we’re spending an ordinary afternoon and quietly decide whether our good version is showing up, or whether we’ve filed that for later.

I’ve found the most honest test is small. Not “am I living my best life,” which is too big to answer. Just: the next thing in front of me, the reply I’m about to send, the tone I’m about to take with someone I love, is that the good version, or the tired version borrowing against a tomorrow I’m assuming I’ll get? Most days I catch myself borrowing.

The point of the maxim, for me, is the catching.