In our modern lives, we instinctively reach for a physical challenge—something hard and impressive—to help us cross an emotional chasm.

You get divorced, you climb a mountain. You recover from cancer, you run a marathon. We might not be able to articulate exactly why we’re doing it. We may not have the exact formula to drive the best outcomes. But year after year, generation after generation, we lay down gauntlets for ourselves and work to cross them. Our ancestors always have. And new science is telling us why it works.

Lisa can smell the river, feel it in the air—long before she can see or hear it. As the lead runner, she sets the pace for all six in her group as they descend in darkness toward the Carbon River. The temperature drops. It’s pitch black as they tack downward through the valley—the pockmarked dirt trail lit only by the circular beam from her headlamp. This is no everyday hike. Lisa is in the 18th hour of a continuous 150K (~93-mile) run around Mount Rainier in Washington state. She and her team will run clockwise around the mountain, on a single-track trail typically used for a strenuous hike of 7 to 14 days. Across ridges, peaks, and valleys, they’ll climb and descend a total of 27,000 feet in 45 hours before they’ll sleep again.

Suddenly, Lisa feels a sharp prick of pain on her ankle. In the disorienting darkness, she can’t see what struck her. What is this? A stinging nettle? She’s encountered these tall plants with toothy leaves before. In her memory, the sting strikes fast but dissipates quickly. But this pain? It doesn’t stop. It throbs. Moments later, she hears a “cacophony of expletives” behind her. Lisa has unwittingly kicked a beehive. Everyone behind her gets stung multiple times—including their trail guide, Jenny, who’s allergic. They all keep going.

Lisa Hallett organized this epic physical challenge to commemorate the 15th anniversary of her husband’s death. Captain John Hallett died, along with 40 other soldiers in the 5-2 Stryker Brigade, during a peace mission to Afghanistan in 2009. John deployed July 11th. Heidi, their third child, was born August 2nd. On August 5th, John and Lisa spoke by phone. “I remember John said to me: ‘I’ve never heard Heidi cry.’ And I said: ‘Don’t worry. You have a lifetime for that.’” Three weeks later, John was gone, killed by a roadside bomb while delivering medicine to an Afghan village struck by a cholera outbreak.

In the weeks that followed, Lisa felt herself unraveling with grief. Her head was cloudy, her tears uncontrollable—so she started running. “I still remember that first run I went on after John died. It was sunny and it felt wrong that the day was so beautiful, when my heart felt so dark.” But she knew she needed to run. “The runs got even longer, because I could go out and feel my really big feelings and then come home and be that mom who my children needed and deserved.”

Every Sunday since, Lisa has organized a commemorative group run—a tradition that now reaches thousands with her nonprofit organization, called “wear blue: run to remember.” And every year, around the anniversary of John’s passing, she organizes an epic, limitpushing physical challenge. “That’s how I process. It’s very tangible to me.”

And this downhill trail, in the dark, covered in bee stings, is definitely tangible. They’ve run 45 of 93 miles, and Lisa can hear the river now—rushing, tumbling, loud. The temperature drops again, a sign they’re getting close. They step out on an outcropping of rock, water rushing below. Then Jenny says, “Follow me,” and leads them through the darkness to the riverbank and bridge. Except it isn’t exactly a bridge. It’s just a log. A slippery log, no handrail. One by one, they cross. Lisa is last. She crawls on all fours. “We make it across, and there’s that release of knowing, ‘We did it, we did it.’”

Just 48 miles to go.

I asked Lisa to tell me this story, in detail, start to finish, because I want to understand what drives people to take on an epic physical challenge. As I researched across cultures and time, these challenges kept reappearing in different rituals—in coming-of-age rites, in initiation rites, in pilgrimages, in festivals. They took the form of physical exertion, feats of strength and speed, voluntary fasting, immersion in heat or cold. For a modern American sensibility, they don’t always make logical sense. But they’re nearly universal and remarkably persistent. I wanted to understand why.

I asked this of Lisa: Why take this on? What do you get from it? “The physical challenge, it’s this chance to become more than my loss, more than this moment, more than I am right now,” she tells me, carefully choosing the words that might capture the power of these defining moments. “Life gave me hard that I didn’t choose. But when we make the choice—when we choose hard and let that hard redefine what hard means in our lives—it gives us back our power.”

By throwing down the gauntlet, by pushing herself physically to the brink, Lisa believes she can prove something to herself about herself. She can become the person she needs to be.

And the science tells us: She’s right. As Lisa circled the mountain on the 15th anniversary of her husband’s death, she didn’t just metaphorically mark a milestone in her life. She biologically reset her body and brain. Over the last 20 years—using new technologies that let us see inside the brain and inside our cells—scientists across different disciplines and geographies have come to the same understanding: An epic physical challenge— known in scientific terms as hormetic stress—creates a cascade of changes in the body that trigger profound renewal, repair, and growth. An epic physical challenge, correctly undertaken, can literally change what your body and brain are capable of.

Challenging, visceral physical experiences were common in the ancient world, deeply woven into the spiritual landscape of life. There’s the coming-of-age ritual—a test of stamina, strength, and courage for young men, in particular, to prove their worth. There’s the pilgrimage—an extended, challenging journey to arrive at a sacred place, for personal transformation. And there’s the ancient festival, with its physical exertion and its many varied requirements for sleeplessness, darkness, dancing, fasting. It was understood: Spiritual transformation—perhaps all transformation—begins with the body.

And we still seem to know this, intuitively, today. In our modern lives, we instinctively reach for a physical challenge—something hard and impressive—to help us cross an emotional chasm. You get divorced, you climb a mountain. You recover from cancer, you run a marathon. We might not be able to articulate exactly why we’re doing it. We may not have the exact formula to drive the best outcomes. But year after year, generation after generation, we lay down gauntlets for ourselves and work to cross them.

These days, we’re taking on these epic challenges in epic proportions. Extreme sports are on the rise, and they’re more accessible than ever. More people walked the European pilgrimage route Camino de Santiago in 2025 than in any other year in history. There were 529,386 official pilgrims—all of them traveling at least 100 kilometers (~60 miles), many close to 500 miles. Hundreds made the journey in wheelchairs. Those numbers grew 100% since 2015 and more than 33,000% since 1986, when just 1,592 walked the route. Marathon participation is also rising dramatically. The 2025 New York City Marathon broke a world record with 59,226 runners—more than 1,000 times larger than its first race, in 1970, when 55 finished. “It went from being something for fanatics to the everyman’s Everest,” marathon specialist David Monti told The New York Times. And even Everest itself has nudged closer to an everyman endeavor. There were more than 800 summits in 2025 (just short of the 2019 record)—a now-infamous crush of climbers straining toward the top of the world.

You might initially recoil from these trend lines. You might dismiss the epic physical challenge as a testosterone-fueled dominance display or a flex on TikTok. But the epic physical challenge is so much more than that. It isn’t just driven by ego. And it isn’t just symbolic. A carefully calibrated, limit-pushing, physically demanding challenge—serious physical exertion, extended fasting, exposure to extreme heat or cold—creates a profound biological reset in the body. It’s as if the stressor signals: Conditions have changed! Get ready! You need to adapt!

This reset is caused by what’s known, scientifically, as “hormetic stress.” This is not the everyday emotional stress of deadlines or bills or social events. This is physical, biological stress, and it results from an encounter with something so dangerous and threatening it could cause physical harm or even death, if unchecked.

“Hormesis is really the science of good stress,” says Sharon Horesh Bergquist, a doctor and researcher at Emory University. “So it’s the science of how the right kinds of stress in the right amounts and for the right duration—followed by a period of recovery—can help us grow and become stronger.” Sharon studied biophysics and biochemistry at Yale and graduated from Harvard Medical School. She wrote the 2025 book The Stress Paradox to help people understand this counterintuitive idea about human thriving.

“Our bodies are actually designed for intermittent stress,” Sharon says. “Periods of stress followed by recovery, stress followed by recovery. We were made to do these hard things.” The hard things, she says, are actually not optional. They’re required to keep the human body running well. And it starts with our cells. “What happens at the level of our cells when we experience stress is more than just a fight-or-flight response,” Sharon explains. When cells are under stress—not just any stress, but hormetic stress—their response triggers healing, repair, and regeneration.

Different types of hormetic stress—exercise, fasting, heat—have slightly different effects. But often, DNA is repaired. Often, inflammation throughout your body goes down. Often, special proteins are created to protect and patrol the body. Supercharged immune cells called “natural killer” cells are released, which help fight disease. In some cases—particularly during an extended challenge—the body recycles old and damaged parts through a process called autophagy, sometimes compared to “spring cleaning” at the cellular level.

So an epic physical challenge does renew and recharge you. And in some ways, we humans have always known this. “We’re just now explaining what’s happening in your biology—how you’re actually literally renewing your cells,” Sharon says. “It’s not just a sense of renewal in a very abstract spiritual way. You’re making your body feel and function better. You’re discarding the damage. You’re discarding these older cells. You’re literally rewiring your body.”

After 45 hours and 93 miles, Lisa finished her run at 2:45 a.m., alongside her fellow runners Lee Yoneyama and Lisa Blake. For the last three miles, her daughter Heidi and two friends also ran by her side. “We get to the finish line. Jenny and Misty are there and they’re holding signs,” she tells me. “And we knew: We had finished. We ran around the mountain.”

Something struck me about Lisa’s description. It was her words, ‘We knew.’ How, exactly, did she know she was done? There’s a finish line, yes. Always helpful. But even more so: the friends. The friends holding the signs and shouting, ‘You did it!’

I’m not sure I can point to a specific scientific study that proves this next statement, but it seems that we humans have an ancient and biological need for our achievements, our sacrifice, to be witnessed by our community. In today’s social media world, we’ve become so addicted to this witnessing, this approval, that it’s perverted our perception. We castigate ourselves for any desire to be seen. But maybe the urge itself isn’t hedonistic. Maybe, at its core, it’s communal. We yearn to be of service. We look to others to tell us if we’ve served. We want our highs and lows to have meaning, and that meaning comes from others.

So if you boil it down, an epic challenge needs two things to have impact. First, as we know, it needs to be hard. And second, that accomplishment needs to be witnessed—it needs to matter to other people.

Adapted from The Great Remembering, published by Authors Equity. Copyright © 2026 by June Cohen. All rights reserved.

About the Author

June Cohen is a pioneer in media and technology, best known as the co-creator of TED Talks, Masters of Scale and Meditative Story. During her 11 years at TED (2005–2016), she co-hosted the flagship event—working with hundreds of speakers on their talks—and launched TED Talks online. She’s earned 100+ industry awards for her work, including 67 Webby honors, 8 Apple “Podcast of the Year” Awards, and a Peabody.