It all started over a midmorning beer. Pete Kostelnick, a whippet-thin financial analyst from Lincoln, Neb., had just won one of the toughest races on the planet, the Badwater 135, a 135-mile run from Death Valley to Mount Whitney, Calif.

He sat in a parking lot with a childhood friend, sipped his beer, and made the gutsiest decision of his life: “I’m going to go for the transcontinental record.”

On Monday, Kostelnick broke the world record for fastest run across the United States (the feat is expected to certified by Guinness World Records.) The previous record, held by Frank Giannino since 1980, was 46 days, 8 hours and 36 minutes. Kostelnick finished the roughly 3,100-mile San Francisco to New York journey in 42 days, 6 hours and 30 minutes, four days faster than anyone else.

Kostelnick’s early running history was unremarkable. He spent college hitting the books instead of the track. Unhappy with his weight, he caught the running bug. He eventually completed a slew of marathons, including the Boston Marathon and Colorado’s Pikes Peak Marathon. He set his sights on going longer.

How do you train to run across the United States? You need to run. A lot. In the month preceding the start of his transcontinental run, Kostelnick logged over 900 miles. During the workweek, he would run at least 30 daily miles, split between a morning and an evening run. “I figured out a pretty efficient system,” he said. “I could be running four minutes after I woke up.”

The weekends involved a bit more, with a 50-mile run on Saturday and a 40-mile run on Sunday.

“He sort of happens to be the right man at the right time to go for the transcontinental record,” said Chris Kostman, director of the Badwater 135 ultramarathon. “He’s a humble guy who has natural talent, plus the drive and ambition to do something with it.”

I wanted to get a front-row seat to watch the breaking of this record. I also felt compelled to support a friend and fellow ultramarathon runner. I served on Kostelnick’s crew at the 2015 Badwater ultramarathon, where I ran 40 miles with him across the searing Death Valley desert. I loaded up my S.U.V. and headed toward Bowling Green, Ohio.

I met my friend at 10:35 a.m. on his 36th day of transcontinental running in an R.V. parked next to a bike path. He had just finished his first run of the day. Before he set foot in the R.V. for a break, he took a marker and updated a small whiteboard he called his “roar board.” He checked the two GPS watches he wore, along with a third GPS tracking device he carried. He and his crew kept meticulous records, which included posting his route, his GPS data, and making daily videos of the run, all of which will be checked and verified by the Guinness Book, which will certify the record.

Kostelnick recorded the 42.5 miles he had just completed, along with his start and stop time. Trasie Phan, who served as the trip’s logistics coordinator, said that only Pete could touch the roar board. “He told me the only other people allowed to touch it were Katy Perry and David Hasselhoff.”

Kostelnick wolfed down a few thousand calories, shoveling beef stew, a protein shake, protein bars and chocolate-covered toffee into his stomach as if it were coal entering a fiery furnace. We were ready for his second run of the day.

The first few miles were uneventful. We chatted about our families, he asked me about my work and running and we tried to decide whether Ohio was actually part of the Midwest. “It’s so great to have you here,” he told me. “This has been one of the lowest days of the whole run. With you, I can just relax and take it easy.”

The renowned ultramarathoner and author Dean Karnazes had a similar experience when he completed his transcontinental run in 2011. He said most people asked him practical questions about his run, wondering what he ate and how many shoes he wore out. “You don’t really have meaningful conversations,” he said. “Psychologically, that’s hard to deal with.”

“I think of each day as its own episode,” Kostelnick told me. “Today is Episode 36.” Mentally, he said he splits the day into four chunks of mileage along the lines of 20-20-20-10. By running a steady pace, he maximized his daily rest. “Each day I try to stay off of my feet for 11 hours,” he said. “I’m not the best sleeper. Most nights I get six hours.”

We continued at a comfortable pace, stopping along the way to receive sips of soda, water and salty and sweet food. While it may sound strange, drinking soda is fairly common in ultramarathon running. We drink it because it’s an easy way to get calories and often caffeine. The carbonation can also help settle your stomach. When you’re burning more than 7,000 calories each day you can’t have the same health conscientiousness that you normally do.

We were supported by members of Kostelnick’s crew, Chuck Dale and Dean Hart. Both are ex-military and ooze discipline. At one stop, I spied Chuck flossing on the side of the road.

They also don’t spook easily. You would have never known that the previous day both Chuck and Dean nearly lost their lives. In the early hours of Episode 35, a large truck smashed into their support vehicle, totaling it. Chuck and Dean were unharmed, even though Dean was seated in the car. They didn’t panic, found a running fan who agreed to lend them his car, and kept on moving. Pete continued to run.

I began to understand something I heard from Charlie Engle, the accomplished ultrarunner who recently released a book, “Running Man,” that describes his short stay in prison after what many people think was an unjust conviction for mortgage fraud. Engle, ever the multitasker, completed our 30-minute interview while running.

“Having a solid crew is the single most important aspect of taking on a record like this,” he said, as I heard cars in the background whiz by. “Think of that major accident to their crew vehicle. Anyone can look at a tough situation and say, ‘Oh my God, the sky is falling.’ It’s a rare individual who can face that kind of adversity and have it not be a bump in the road.”

At this point I realized that I was witnessing a cluster of rare events and even rarer individuals, who faced a daily constellation of hassles and successes, all with the same goal of getting Kostelnick to New York as quickly as possible. It was magical and menacing, inspirational and aspirational, pure and purposeful. I was watching the making of history.

To complete the fastest-ever run across the United States, you need more than talent, guts and grit. You need more than a talented support crew, sufficient food (whether it’s 2,000 or 15,000 calories a day), and a place to rest. What you need is the ability to make others feel part of something greater than themselves.

Kostelnick may be the world’s real Forrest Gump. His record-breaking run and upbeat, humble demeanor send positive ripples into others’ lives. “Hearing about a tremendous feat like Pete’s can inspire and motivate people to live healthier and more adventurous lives,” said Karnazes. “That is the greater good our sport provides to humanity.”

Still, Kostelnick is human. As he stood on the steps of New York’s City Hall, he hugged his wife and fought back tears. “I’m not running back,” he said.