New York City was my first marathon. I finished in 3 hours and 38 minutes. I was happy with that time, a good first outing for a middle-aged runner. Sure I’d gotten crampy and slow coming up 5th Avenue near the park; and sure I’d puked at the finish and had to visit the medical tent; and sure I’d fallen asleep on the dinner table that night—but all those represented opportunities for improvement, I figured. For most runners, the first marathon is a rough draft, and their subsequent efforts show steady improvement until they reach their optimal race. I was looking forward to discovering how fast I could get.

The second time I lined up for the marathon, it was with a much better base of training and a lot more race intelligence. Not only did I have one marathon under my belt already, but I’d also run a few other shorter races, so I was no longer distracted by race-day nerves. I took off over the Verrazano Bridge feeling steady and calm even in the face of high winds and flying garbage. I felt good all the way until I’d crested the Queensboro Bridge, 16 miles in, at which point my legs started slowly losing steam and my mind started attacking itself. By the time I reached Central Park, I was keeping o.k. time but I was feeling thoroughly dispirited. I decided a strong final push would help me feel better about my race, so when I saw the 1/2 mile banner, I went all out, picturing myself on our neighborhood track running repeats.

I made it about 400 yards and then stopped like I’d been shot. I folded over at the waist, my hands on my knees, my heart beating so fast I could feel it in my ears. “Duuuude! Don’t stop now!” someone yelled from the sidelines. “You’re almost there!” But I was no longer in charge of myself—something else had taken over. And frankly I was scared of it. It let me go a minute later, and I ran—staggered—to the finish line. I fell into the arms of a volunteer who saw me teetering like a drunk and raced to ask me if I knew my name and the date. I did know my name and the date, but my tongue felt so swollen I could only answer with indistinct grunts, as if my mouth were full of dry bread. The volunteer whisked me into the medical tent (again!), where I was promptly laid out on a gurney and connected to a saline drip (“same thing we use for hangovers in med school,” the doctor assured me). Within minutes I was feeling well enough to realize that I hadn’t checked my time yet. I fished my phone out of my pocket and looked up the results on the marathon app. I’d run exactly the same time that I’d run the year before: 3 hours, 38 minutes.

Now I was obsessed. Two years of the exact same time was a fluke, an absurdity. I’d put it behind me with one more strong effort. Over the next year, I trained like I’d never done before, studying nutrition and tactics, putting in lots of cross training miles. When July rolled around, I followed a training plan to the letter for the next 4 months. The week of the marathon I was as prepared as I could possibly be. I felt great. The weather forecast was good. On top of everything else, my assigned race number was our family’s lucky number–a number that has followed us around auspiciously for almost 60 years.

But the night before the race I was racked with inexplicable anxiety, the kind that only my fellow insomniacs can appreciate fully. When I finally decided to get up and start preparing for the race, I hadn’t slept for one second. I immediately put all my race goals on the shelf, decided I’d give myself permission to quit midway through if I didn’t feel right, and drank as much coffee as I felt I could safely consume. I tried to enjoy the absurdity of it, and tried to be thankful for every mile I made it through in one piece. When I surprised myself by somehow making it to the finish, I was somehow not surprised to see a familiar sight there: my race time, 3 hours and 38 minutes.

Why work hard at something if you’ll never be any good at it? I’d grown up believing that way through life was to discover your strengths, then throw all your efforts at them to see how good you could get. Growing up was a process of winnowing your interests, clarifying your desire, focusing your talents. There was no accounting in this scheme for unrequited love. I started out my marathon-running life believing that maybe I had a special knack for it; now I found myself scouring the internet for a quiz that would explain to me what—if any!—sport I would be good at, since running clearly wasn’t the one (I found such a quiz, by the way. The answer was judo).

One rational response to realizing that you’ll never be a contender might be to feel relief. Rather than bury yourself in pressure to improve, you could free yourself from expectation and revel in the fact that you’ve found a hobby you enjoy. Quit racing, start running for the joy of it.

I’m sorry to say that I didn’t have that rational response. Even with nothing to win, I keep training for races with the single-mindedness of a person determined to come as close as possible to success.

But it’s not because I secretly believe that I might break through, Yuki Kawauchi-style, and stun the world with a victory. I know that I have limits—and it’s because I know I have them but don’t know what they are that I keep training. How would I discover my limits if I didn’t run as though I had something on the line? Sometimes even when I think I’ve found a limit—like my heart pounding out 210 beats per minute—it turns out not to be as fixed as it first appeared. I don’t want to feel my heart beat that fast again, but I’ve learned how to run faster and longer without hitting that limit. What my heart was telling me in that second marathon was not “you can’t go faster than this,” but “you can’t go faster than this right now.”—it was not laying down a general rule, not enforcing an absolute limit but a limit under a very particular set of conditions. If I hadn’t kept at it, kept trying to get faster after that scare on the course, I would never have learned that, would never have learned that even my own body can be an unreliable narrator, that even when it says something that appears unambiguous, it actually requires interpretation like any other information.

That, it seems to me, is the whole point of testing our limits. Not simply to find out how much we can accomplish but to change the frame around the way we perceive ourselves and what we do, change the context in which we understand ourselves. For example, while I’ve continued to suffer from insomnia since my sleepless marathon 4 years ago, I’ve never again lain awake anxious about my insomnia itself. Even if I don’t sleep, I’ll get by—I know that now, in a way I’d never have known it without running that race.

Nor would I have learned that, in spite of three years of evidence to the contrary, 3:38 was not my limit for the marathon. A couple of years after that third marathon, I went home to South Carolina and ran a 3:24. Five years had passed since I’d first run, mid-life years of inexorable physical decline, or so we’re told. Time was running out for me, surely. And yet I broke through so emphatically that I it filled me with optimism: what else could I do that I thought I couldn’t do? If 3:38 wasn’t my limit, what was?

I’m testing my limit again soon—in three weeks, I’ll run my first road marathon since my breakthrough in South Carolina in 2017. I’ve run plenty of races since then, ranging in distance from 1 mile to 50 miles, but the 26.2 miles of the marathon are the baseline test for me. I have no idea how I’ll do. I’ve been preparing for it as though I can still run the fastest marathon of my life, as though my limit has not yet been reached.