Stoicism emerged in the third century B.C. in the works of the philosopher Zeno of Citium, who influenced successors like Seneca, Epictetus, and the emperor Marcus Aurelius with his teachings about virtue and equanimity in the face of suffering. Its current vogue owes much to the imprimatur of the Valley’s own philosopher king, 4-Hour Workweek author Tim Ferriss, who championed a book about Stoicism, The Obstacle Is the Way, by marketing savant Ryan Holiday, and made it a must-read among lifehack fetishists.

Since then, the fad has taken on a life of its own. Susan Fowler, the Uber engineer whose blog post about sexual harassment touched off a chain of events that culminated in the resignation of CEO Travis Kalanick, said Stoicism emboldened her to speak out. Y Combinator put A Guide to the Good Life: The Ancient Art of Stoic Joy by William B. Irvine on a reading list for entrepreneurs, alongside books about the founding of Bell Labs, Nike, and Pixar. A rare rave from Recode editor Kara Swisher helped popularize an app called WeCroak, which sends users push notifications featuring Stoicism-flavored meditations.

Inevitably, many of these neo-Stoics are the same people who think the natural human lifespan is just another challenge to overcome, which is awkward, because if there’s one thing the Stoics were crystal-clear on, it’s that death is something not to avoid but to accept and even welcome. “The man who fears death will never do anything worthy of a man who is alive,” as Seneca put it.

“The Stoics are really about a kind of letting go,” says Nancy Sherman, a professor of classics and philosophy at Georgetown and author of Stoic Warriors: The Ancient Philosophy Behind the Military Mind. In the Stoic ideal, a wise person is one who seeks only to be virtuous, since virtue doesn’t require health, wealth, or anything else contingent on luck or circumstance. “When you start talking about ‘How long am I going to live?’ and ‘Am I going to be in the first cohort of immortal folks?’ it starts sounding like you’re messing with the wrong stuff,” Sherman says.

“The Stoics probably talk about death and the inevitability of death more than just about any other topic,” Ryan Holiday says. Stoics not only accept the reality of death; they force themselves to confront it at every turn, meditating on it in a practice termed memento mori. “Cicero said to philosophize is to learn how to die.”

Bill Irvine, a professor of philosophy at Wright State University in Dayton, Ohio, has been surprised to watch his book become a touchstone for a generation of entrepreneurs. “When I hear the directions they want to head, it dawns on me that they have a different understanding of Stoicism than I do,” he says. “It sounds to me like they’ve accepted some aspects of Stoicism, but then other aspects they choose to ignore. For instance, this thing of not clinging to life.”

Like the math that limits how many bitcoins can be mined — to use an analogy many born-again Stoics would appreciate — life’s finitude is what makes it feel precious. “Anything you have an infinite supply of is going to be wasted,” Irvine says. “In fact, if you say that there is a heaven and therefore a kind of immortality, a Stoic is going to be suspicious even of that.”

Contrary to the casual usage of the term to mean patient suffering, Stoicism was intended to be a strategy for finding satisfaction and meaning in life by distinguishing between the things that cause suffering, which we may be powerless to change, and the suffering itself, which is often a product of expectation or ego. As Epictetus put it, “The chief task in life is simply this: to identify and separate matters so that I can say clearly to myself which are externals not under my control, and which have to do with the choices I actually control.” Foremost among the externals is when and how life ends, and not just one’s own life, but also the lives of friends and loved ones.

“Stoics accept death,” Irvine says flatly. “For them, it’s going to happen. I’m not at all convinced that they would have thought overcoming it was a wise thing to even strive for.”

Fowler, the software engineer who used to work at Uber, has a theory about the popularity of the philosophy among transhumanists and lifehackers. “It’s peddled as a ‘lifehack’ out here (gross),” she emails. “It has been trendy, largely, I suspect, because people take away from it the idea of ‘Who cares what other people think? It’s all about me and my control over things.’” Fowler points to Seneca’s text The Shortness of Life as evidence that “if they were real Stoics, they wouldn’t be into the longevity stuff.”

Irvine thinks it’s about the love of the hack. Compared with something like Buddhism, which can take decades to understand and master, the basic tenets of Stoicism are relatively easy to learn, and the potential benefit — less suffering — seems to be a state worth striving for. “You can try it this weekend and you’ll know whether or not it’s working for you,” he says. “If you’ve got a very practical-minded, rational person who wants a solution that works now and not in 20 years, Stoicism is very good for that.”

That’s how Geoffrey Woo sees it. Woo is the founder of HVMN, which makes supplements that aim to enhance mental and physical performance. He’s an influential figure in San Francisco’s biohacking community, leading a weekly intermittent-fasting meetup that draws hundreds of attendees. (Among the benefits attributed to intermittent fasting are longevity-enhancing changes in gene expression and mitochondrial activity.)

In Stoic teachings on death, such as Marcus Aurelius’ exhortation to “execute every act of life as though it were your last,” Woo sees a parallel to Steve Jobs’ oft-quoted 2005 commencement address. In that speech, the Apple co-founder, already sick with the pancreatic cancer that would kill him, praised death as “the single best invention of life” and exhorted his audience, “Your time is limited, so don’t waste it living someone else’s life.”

Thinking in those terms “is a very good heuristic for making life decisions,” says Woo, likening it to the “regret minimization framework” used by Amazon’s Jeff Bezos. “It’s a way to have a short-term focus, a clarity of vision of what you want to do now while preserving the optionality of having more time.”

When I interviewed Thiel in 2015, he also brought up Jobs’ speech, but only to challenge its assertion that mortality is motivational. “I believe the exact opposite of that,” Thiel said. It’s the imminence of death, not obliviousness to it, that encourages complacency, he argued. He brought up a grand-uncle who, at 85, had said he would have gotten a few more PhDs if he’d known he would live so long. “Maybe it’s when people think they have no time left that they don’t undertake things.”

Whichever argument you find more persuasive, it’s noteworthy that both couch the idea of making the most of one’s time on earth, whether by getting more out of each day or by getting more days. In Silicon Valley’s cult of productivity, historically spiritual practices such as meditation, fasting, and psychedelic drug use have all been pressed into the service of crushing it at work. Philosophy is just one more time-management technique, like the Pomodoro time-management method or drinking Soylent at your standing desk.