“The present is all that they give up, since that is all you have, and what you do not have, you cannot lose.” That is Marcus Aurelius, in Gregory Hays’s 2003 translation, writing to no one but himself. The Roman emperor, who lived from AD 121 to 180, kept a private notebook of reflections we now call the Meditations. The line in the title comes from Book 2.14. I find it a strange sort of comfort. It reads less like advice and more like a piece of arithmetic.

I’m not a psychologist or a philosopher, and what follows is reading and reflection, not instruction. The Stoic passages here are arguments Marcus was making to himself about death and time, not proven facts about either. The one modern study I lean on is a single, correlational piece of research, not settled science. Read it all as a way of thinking, not a prescription.

The George Long translation puts the same thought this way: “no man loses any other life than this which he now lives, nor lives any other than this which he now loses.” The wording differs, but the point does not: the present is the only moment you ever hold.

Aurelius builds the argument to a point. Since the present is all anyone can lose: this instant, and nothing more. The past is already gone and the future was never yours. What sounds like consolation for turns out to be a claim about how little of life we hold at any given second.

You can resist this, and I did at first. Surely a long life is more than a short one. Surely we own our memories and our plans. But the Stoic reply is precise: a memory is not the past, it is a present act of remembering. A plan is not the future, it is a present thought about it. Everything you have ever experienced arrived as a present moment and left as one.

Aurelius was not the only one to notice this. The idea sits inside a long line of thinking. Centuries later, psychologists went looking for whether living in the present has any measurable link to how people feel. In 2010, the Harvard researchers Matthew Killingsworth and Daniel Gilbert noted that same inheritance in a Science paper: “Many philosophical and religious traditions teach that happiness is to be found by living in the moment.”

Killingsworth and Gilbert built an iPhone app that pinged people at random moments to ask what they were doing, whether their minds were on it, and how they felt. They found that people spent 46.9 percent of their waking hours thinking about something other than what they were doing. That is nearly half of waking life, spent somewhere other than where the body is.

Their headline conclusion was blunt: “A human mind is a wandering mind, and a wandering mind is an unhappy mind.” Killingsworth went further, arguing that “how often our minds leave the present and where they tend to go is a better predictor of our happiness than the activities in which we are engaged.” That is a strong claim, and I’d hold it lightly. It rests on one dataset, and it shows a link, not a cause. The study’s timing analysis suggested that mind-wandering came before unhappiness, but that is a clue, not a law.

What strikes me about setting the two side by side is how little the problem has changed. Marcus was writing about a mind that drifts into dread of the future and regret over the past. Killingsworth measured the same drift with a phone. The measuring tools differ, but the wandering they describe is the same.

Stoicism does not ask you to empty your mind or to stop planning. Marcus planned constantly; he ran an empire. What the passage asks is smaller and harder: to notice that the only life you have is the one happening right now, and to stop treating it as a rehearsal for something that arrives later.

If the present is the only thing you ever hold, then it is also the only thing you can ever lose, whether you live to thirty or to ninety. The long life and the short one are, in the only currency that counts, the same size.

A reminder to live in the present is not a substitute for a qualified counsellor or therapist, and it is worth reaching out to one if  low mood, or intrusive thoughts about the past or future are persistent, interfering with daily life, or something you find hard to manage on your own.