In 1990, I spent two weeks at the Formula One circuits in Estoril, Portugal, and Jerez, Spain, writing about one of the most intriguing athletes to ever live, Ayrton Senna da Silva. Of course, all I wrote about, and all anyone who covered him could talk about, was his relationship with death. Senna’s belief in God and his mortality glowed like an aura about his impossibly handsome head, and every day on the track he did the unthinkable because he was undistracted: No matter what team, no matter what car, he considered it his only job to find his physical limit.

Asif Kapadia’s new documentary, “Senna,” which opens in L.A. on Friday and tracks the driver on an inexorable rocket ride to three world championships in four years, captures his soft-spoken intensity perfectly. Most moving is the comment of F1’s lead physician, Dr. Sid Watkins, who read that aura and, after the death of driver Roland Ratzenberger in 1994, begged Senna to quit and just go fishing with him. But Senna was locked into an exploration of being human that few will understand.

A story from the track, touched on in the film, makes that clear. I was in the press room in Jerez when suddenly on the TV came images of Martin Donnelly, a driver for Lotus, lying on the sunbaked track, still strapped in his seat after his car had disintegrated, his legs mangled in all the wrong directions. I wrote that he looked for all the world like an astronaut that had fallen to Earth, and he was dead. A trackside fireman touched his helmet and backed away.

I bolted for the track, and right beside me, running out of the pits, was Senna. Just the two of us. We ran to the fence and leaped up on it, clinging there. He had a stricken look on his face as we watched the paramedics bring Donnelly back, find a pulse, load him off to the hospital. Senna then walked back to the pits, suited up, and sat in his car, the mystical calm settling back over his face.

The track was cleared again for qualifying, and other drivers, including the fearsome Ferrari team with their new touch shifters, chose not to run. But the first one out was Senna. He didn’t seem angry. He seemed to be in a dialog, he and the car talking to something bigger, his Honda wheezing like an attack fighter. He eclipsed the lead time by an eternity, took poll position, then parked, unsuited, and walked to the hospital.

A doctor came out and announced that Donnelly would live. After a while, Senna walked out and I followed him back to the pits, where he burst into tears.

In 1994 at San Marino's Imola circuit, the day after Dr. Watkins tried to get him to quit, Senna flew into a wall in sixth gear and died of a head injury, apparently the victim of a car malfunction. The intriguing proposition made by Kapadia’s film, and what I saw with Senna, was that he never did find his limit. Given the right equipment, he could have gone faster. Even at the end of such an epic story, one is left saying, oh, what might have been.