I had the most magical experience a few weeks ago.

It wasn’t exactly time travel, but it felt like something close.

I was sitting down to work on a chapter for my next book (btw, ​the third book​ in the Stoic virtue series comes out in June. I’m working on the fourth now). I had decided to write a chapter on the importance of keeping what’s called a ​commonplace book​.

I sat down at my desk, pulled out my notecards, and found an old, worn notecard mentioning something that Joan Didion had written about notecards from a chapter in her book ​Slouching Towards Bethlehem​. I walked over to the shelf and pulled it down and of course, there it was, a beautiful essay in that book called “On Keeping a Notebook”, written in 1966.

I got goosebumps, not just because it was exactly what I needed, but because I happened to be sitting, at that very moment, in Joan Didion’s chair (​I bought it at a charity auction​ after her death). How did I know, nine years ago when I read ​Slouching Towards Bethlehem​, when I took the time to jot that little reference, that it might be of use to future-me?

“Why did I write it down?” Didion herself asks in that essay. “In order to remember, of course, but exactly what was it I wanted to remember?”

I don’t know, you never really do, but the process of finding, years later, the perfect thing that I had recorded in the margins of a book or a notebook, has happened to me so many times now that I’ve begun to question the time-space continuum.

When I was writing ​Courage is Calling​, for instance, I decided I would write about the Spartans at Thermopylae. I went to my shelf again and found there, in my ​Penguin Classics edition​ on page 477, what was effectively a highlighted outline of everything I needed to write this section…which had sat there silently for nearly twenty years. I didn’t even think I would be a writer when I read that book! I was just reading something that I thought was interesting!

This happens time and time again. One of my favorite books to re-read is F. Scott Fitzgerald’s ​The Great Gatsby​. I love ​Gatsby​ not just because it’s an incredible book, one of the great works of the English language. I love it because it was one of the first books I ever loved. I was assigned to read and write an essay on ​Gatsby​ in my sophomore English class and I still have that copy. So when I re-read ​Gatsby​, I’m not just talking to Nick Carroway and Jay Gatsby and Meyer Wolfsheim and Scott Fitzgerald himself, I am also talking to 16-year-old me. I can see the food I spilled while I read it at the kitchen table of my parent’s house. I can see my teenage handwriting in the margins.

I can also see the things I noted when I re-read it in college. I can see the notes I took when I read it in my twenties. I can see how I barely noticed the passages on page 73 the first few times I read it and I can see myself flipping back through the book to find them in 2016 when it suddenly hit me that the scene with Meyer Wolfsheim–a stand-in for the gangster Arnold Rothstein, fixer of the 1919 World Series–would be perfect for the opening of the book I was writing about Peter Thiel’s secret lawsuit, the book that would become ​Conspiracy​.

Even as I write this paragraph right now, I have ​Gatsby​ on my desk to revisit some of my favorite pages. I’m struck again by those first few sentences that I’ve read dozens of times: “In my younger and more vulnerable years my father gave me some advice that I’ve been turning over in my mind ever since. Wherever you feel like criticizing anyone, he told me, just remember that all people in this world haven’t had the advantages you’ve had.” Those words have different meaning to me today than they did five years ago, let alone when I first read them at 15. Now I have kids, now I have a better sense of my own advantages in life, now I know how hard it is to write something that good without sounding preachy or lame.

The poet Heraclitus talked about how we never step into the same river twice. By that he meant that the river is always changing, glowing evermore towards the sea, and we ourselves are changing, growing, getting older. The pages of a book don’t change, but we change, the world changes around them–we’re able to see and perceive things differently.

That’s one of the things that Didion notes in her essay on notebooks. Notebooks, she said, are a way “to keep on nodding terms with the people we used to be.” They are blasts from the past, reminders of how easily “we forget all too soon the things we thought we could never forget.”

I’ve talked before about my notecard system–which I learned from Robert Greene–so I won’t bore you with it here (​here’s a video about it​). But the reason I try to be an intentional reader, why I try to take notes and record and store what I read, is because I have seen the magic that comes from it, personally and professionally.

The best time to have started a notebook or a commonplace book would have been many years ago, but the second best time would be now. Start small–record what strikes you, quotes that motivate you, stories that inspire you. Don’t think too hard, just follow your curiosity. When you read a book, write in it, fold the pages, really engage with the material. Preserve this moment in time. Capture what you’re thinking and feeling. Your future self will thank you.

“It all comes back,” Didion writes at the close of her essay. More often than not, it will come back to you in ways that you couldn’t have planned for, but that you prepared for.

As a fellow time-traveler, I can tell you she’s right.

So start.

Several years ago I was swimming in a pool in Austin—I wish I could say it was Barton Springs, one of the wonders of the world or even the Los Angeles Athletic Club (photographed above), but it was actually a 24 Hour Fitness off I-35—and a reader recognized me as I was getting out of the water.

I’m reading your book ​Ego is the Enemy​, they said.

That’s funny, I replied, because I wrote it in this pool.

They gave me a weird look, but I think most writers would know exactly what I was talking about.

Having a physical practice is essential to the creative life.

Not just because it gets you up and out of a chair. Not just because it’s good to stay in shape. But because when the body is in motion, the mind can really get to work.

My routine then—it’s a little different now that I have kids, as I’ve ​written​ and ​talked​ about—was to write in the morning until I hit a point of diminishing returns. Then I’d either go for a swim, or put on my running shoes and go for a run. Depending on what time it was or whether I was writing from my home or my office, I ran one of a few go-to routes. The purple, red and gray trails in the eerie elephant graveyard of the burned-out forest of Bastrop State Park. The seven or ten mile loops along Lady Bird Lake in Austin. Or, if it’s already started to get dark, up 11th to do laps around the lit up Texas State Capitol and then down Congress to Cesar Chavez and back.

Lately, I’ve been doing my runs in the morning. I’ve been biking more than I did before ​because of the ankle injury​. I’ve been doing more weight training, too.

I try every day to keep my practice because, as the Jews say of the Sabbath, it keeps me.

Regardless of what time, where, how far or for how long, going on a run or a ride or a swim almost always goes well. With writing, it’s the opposite. Professional writers quickly learn one reality of the job: you have more bad days than good days. It’s the rare day that the writer finds that the words come out exactly the way they were in their head. More often, one is disappointed, distracted, struggling, committed but unproductive. Therefore, the writer needs a physical practice, something that reliably goes well and gives one a sense of accomplishment, to counterbalance the mercurial muses of the creative professional. “The twin activities of running and writing,” prolific author Joyce Carol Oates writes in her ​ode to running​, “keep the writer reasonably sane and with the hope, however illusory and temporary, of control.”

It can hurt sometimes, but even when it does, you feel good after.

A physical practice doesn’t have to be running. “If an action tires your body and puts your heart at ease,” Xunxi said, “do it.” As I said, I like to swim. I like riding my bike. I do weights sometimes. But for you, maybe it’s jujitsu. Maybe it’s yoga. Maybe it’s stand up paddle boarding. But it’s got to be something.

In one of his little books, ​Painting as a Pastime​, Churchill talks about how he discovered painting after a nervous breakdown following the Great War. This little pastime changed his life, got him outside, got him to slow down. “The cultivation of a hobby and new forms of interest is therefore a policy of first importance to a public man,” he explains. “To be really happy and really safe, one ought to have at least two or three hobbies, and they must all be real.”

Hobbies are great, but I do think there is something insufficient about scrapbooking. Photography is cool. So is baking and fantasy football. But in addition to his more cerebral hobbies, Churchill would have also benefited from golf or cycling or tennis, as his famously rotund figure indicates. (He liked to dabble in bricklaying, which I guess counts, but it’s hard to recommend).

At least his painting got him outdoors. He probably had to hike for a few of those landscapes he captured. Still, there is something about cardio–or any form of strenuous exercise–that’s just magic.

One of Churchill’s predecessors knew this well. In ​Stillness is the Key​, I tell the story of William Gladstone, the four-time prime minister of England, who loved to chop down trees on his estate. For hours on end, to escape the stresses of high office, he would head to the forest with an axe in hand. He once spent two full days working on an elm tree with a girth of some sixteen feet. The process consumed him, leaving him no time to think of anything but where the next stroke of his axe would fall.

This arboreal activity was a way to rest a mind that was often wearied by politics and the stresses of life, a challenge for which effort was always rewarded and with which his opponents could not interfere. Without the lessons he learned in those woods—about persistence, about patience, about the importance of momentum and gravity—could he have fought the long and good fight for the causes he believed in? (And to be clear, he would use the wood from these trees and actually his sons sometimes sold chips from them to raise money for charity).

“We treat the body rigorously,” Seneca said, “so that it’s not disobedient to the mind.” That sounds a little aggressive, because in my experience, the physical practice is actually quite kind to the mind. Some days, it turns it off in a very restorative way. Other days, it lets it wander and work on things. I can’t tell you how many times I’ve thought of a great line or solved an intractable writing problem after I stopped writing and went for a run or swim. I even had the idea for this article while on a run through the sleepy afternoon streets of Bastrop, Texas near my ​bookstore​. In any case, it’s a break from screens, from most inputs, and from other people. (Running while listening to a podcast and reading the cable news cirons that scroll across the TV screen at the gym is a nightmare IMO).

The Buddhists talk of “walking meditation,” or kinhin, where the movement after a long session of sitting, particularly movement through a beautiful setting, can unlock a different kind of stillness than traditional meditation. Deliberate, repetitive, ritualized motion, therefore, can serve as an exercise in peace that lays groundwork for creative breakthroughs.

It doesn’t matter what you do. It doesn’t matter where you live. You need to cultivate a physical practice.

Because it centers you. Because it challenges you. Because it’s hard. Because it’s a form of rest. Because it makes you better.

“Obviously the philosopher’s body should be well prepared for physical activity,” the Stoic Musonius Rufus explained, “because often the virtues make use of this as a necessary instrument for the affairs of life. We use the training common to both when we discipline ourselves to cold, heat, thirst, hunger, meager rations, hard beds, avoidance of pleasures and patience under suffering. For by these things . . . the body is strengthened and becomes capable of enduring hardship, sturdy and ready for any task.”

If greatness is our aim, if we want to be productive, if we want to be capable of enduring the affairs of life, we need to take care of our bodies. We need to be strong and sturdy. We need to keep a physical practice so that it keeps us.