Among the many indignities and small dramas that attend endurance sport, the bowel that insists on staging its protest half a mile from any civilized facility, the yawning 5 a.m. alarm that makes a mockery of your better self, none is so momentous, so implausibly heavy, as the moment your index finger hovers over a rectangle that says, with bureaucratic cheerfulness, “Submit.” It is a small button, almost decorative.

Ask anyone who has spent time among bibs and timing chips what they remember most vividly, and you will not always hear about mile twenty, or the taste of salt drying on a winter long run. You will hear about the first time, the first event, the way the webpage seemed brighter than it had a right to be, the way the cursor blinked like a metronome for the heart. It was not merely a sign-up page; it was a one-way mirror, and on the other side stood a version of you that made fewer excuses.

There is a fashionable way to describe the preparation for a marathon or a triathlon or an ultra. We talk about process, about periodization and fueling strategies, about lactate thresholds and “ons” and “offs” and every trick for making an hour pass when the treadmill clock insists it has been eight minutes. We have language for this industry of suffering. We can debate the tensile virtues of carbon plates as if they were family heirlooms. But none of that begins until a tiny leap of faith occurs, a click that is less movement than declaration. That is the moment the sport begins. Everything after is rehearsal.

Before the click comes the committee. It convenes in your head without invitation. Not ready, it says, not fit, not the right gear, not the right time. It reminds you of what happened last time, when your calf tightened at kilometer thirty-two and your will at thirty-three, when the watch died and you ran by instinct and resentment. It floats specters of failure with the officiousness of a parking attendant. It is persuasive, because it is intimate. The committee is made of you, and it has all your old minutes on file.

And then, for reasons I still haven’t quite figured out, you proceed anyway. You type your name as if for the first time. You put an emergency contact, someone who knows you, who will answer the phone with both love and a sigh. You choose a distance that feels preposterous and therefore intriguing. You enter a card number, and the numbers feel like coordinates. You press submit.

There is no fireworks animation. The page refreshes. An email arrives, spare and officious, and yet you stare at it as if it were a deed to some new parcel of land. Perhaps you step away from the desk, look at your hands, and find them unchanged. Perhaps you say nothing at all. But the furniture of the days ahead has shifted, invisibly. You have not only paid for a race; you have hired an accountability you cannot now easily fire. The committee in your head, forced to adjourn, will reconvene tomorrow with new talking points, but for tonight it is quiet.

Endurance sport advertises itself as discipline but converts as compulsion. Once the first entry is made, others assemble behind it like stubborn ducks. A marathon here, another there, as if by spacing them closely enough you might surprise your body into adaptation. You learn things, a catalog of small, durable truths that mostly concern what not to do. You miscalculate, and then you miscalculate differently. What is wrong with you? It is a joke and not a joke. It is also a mirror.

What is wrong with you, it turns out, may be exactly what is right: a willingness to negotiate with fear in public, to accept that the most fragile part of any grand undertaking is not the tendon or the stomach but the mind. The body can be coaxed and trained and bribed. The mind must be tricked, flattered, and, occasionally, ignored. Pressing submit is the first and most consequential trick. It does not dissolve fear; it domesticates it.

After the click, life does not transform into a montage. There are long runs in unfriendly weather. There are pool sessions where your arms feel like rented equipment. There are rides into headwinds so sustained they begin to feel personal, as if the atmosphere harbored a grudge. There are plans scrawled on calendars and then revised and then at times ignored. The early alarms arrive, and you bargain with them until you learn that bargaining is just another way to be late. None of this is particularly cinematic. That is its charm. The days are ordinary; the accumulation is not. Hold steady.

Yet it is hard to overstate the moral importance, the narrative weight, of that first administrative act. To enter is to announce allegiance to a future self whose existence is uncertain and whose demands are inconvenient. It is a vote cast in the dark. When you tell people you have registered (choose wisely), some will clap you on the back, others will look at you as if you had signed a lease on Mars. Most will, in their way, ask the same question: Why? Why this, why now, why you? What’s wrong? The answer matters less than the fact of its pursuit.

If you are reading this while a tab sits open in the background, if you have typed your name once and then deleted it, consider this your gentle shove. The race will not make you a better person. It will not repair the world’s fractures or halt the erosions of time. But it will lend your days a spine. It will give shape to your hours. It will turn questions into experiments. And, when it is over, it will leave you with the odd, durable knowledge that you can choose a hard thing and then do it, which is not everything but is not nothing.

We can do the rest together. That is the point of this project, this chronicle of watts and what’s wrong with them. I will tell you what I learn, which is often what I learned too late. I will try things so that you might not have to, and I will fail publicly so that failure will feel a little less proprietary when it visits you. I will review the gear because this pastime has a way of emptying wallets while promising speed, and it helps to know which promises have any measurable wattage behind them. I am not an expert, and certainly not a doctor. I am an enthusiast with an Internet connection and a tolerance for discomfort that fluctuates with the weather. I will, to the best of my ability, enjoy it responsibly.

But first, the form. First, the little rectangle. You know the one. It is your door. It is smaller than it should be for what it contains. Press submit. The rest of the story is waiting on the other side, patient as a starting line at dawn.