Editor's note (7/20/16): Neil Armstrong died on August 25, 2012 at age 82.

"In my view, the emotional moment was the landing. That was human contact with the moon, the landing…. It was at the time when we landed that we were there, we were in the lunar environment, the lunar gravity. That, in my view, was…the emotional high. And the business of getting down the ladder to me was much less significant."

Neil Armstrong's words to me, in a 1988 interview, came as a real surprise. Like most people, I think, I had expected that for Armstrong, the moment when he took humanity's first step onto another world would have been the ultimate high point of his Apollo 11 mission. As one of the 600 million people who witnessed history's first moon walk on live TV and radio, I remembered my own sense of awe seeing Armstrong's "one giant leap for mankind." And so, when I interviewed him as part of my research for my 1994 book, A Man on the Moon: The Voyages of the Apollo Astronauts, one of the questions I most wanted to ask was how he felt, taking that incredible step. What I hadn't fully realized was that for a test pilot like Armstrong, compared with landing on the moon, setting foot on it was no big deal.

Of all the challenges Armstrong and his crew faced on Apollo 11, the landing itself was far and away the most difficult. Even if there were no malfunctions or other technical problems—an unlikely scenario—the descent would test the abilities of the entire Apollo team, Mission Control, as much as the astronauts themselves. In just 12 minutes, Armstrong and co-pilot Buzz Aldrin had to bring their lunar module Eagle from a height of 50,000 feet, orbiting at a speed of several thousand miles per hour, down to the surface in what amounted to a controlled fall. With no atmosphere, neither wings nor parachutes would have been useful; the only means of controlling the descent was by varying the thrust of Eagle's descent rocket. Adjusting the lander's flight path was especially tricky; with the craft balanced on rocket thrust, changing direction required tilting the entire spacecraft slightly to one side. And as Armstrong and Aldrin were all too aware, there was only enough fuel for one landing attempt. No wonder that before he and his crewmates left for the moon, Armstrong privately concluded that they had a 90 percent chance of returning safely to Earth but only a 50–50 chance of pulling off a successful landing.

And they almost didn't pull it off. The problems began soon after Armstrong and Aldrin began their descent on July 20, 1969. First it was trouble with communications with Earth. Then, alarm tones in the astronauts' headphones signaled something even more serious: the onboard computer, which was controlling the craft's speed and orientation, was becoming overloaded with tasks. Fortunately, experts in Mission Control soon found a way to work around the problem. But the alarms had diverted Armstrong's attention just at the time when he had planned to be watching for landmarks he'd memorized along Eagle's descent path, and scouting for a good landing spot. By the time the computer trouble quieted down and Armstrong was able to look out the window again, he discovered he had a new problem: Under the control of the computer, the lander was heading directly for a football stadium–size crater. The surrounding area was strewn with boulders, some of which were as big as cars.

For a moment—and only a moment—Armstrong was tempted by the idea of trying to set down just shy of those boulders, which he knew would be of great interest to scientists on Earth. But they were going too fast; there were just too many rocks. Armstrong took over from the computer, steering Eagle over the giant crater and the boulder field, and flew onward, hunting for safer ground. While Aldrin read off data on the craft's diminishing speed and altitude, Armstrong scanned the ground ahead. Everyone, in space and on Earth, was very aware that with each passing moment his fuel supply was dwindling.

Finally, Armstrong had found a relatively smooth spot, and with just 100 feet  to go he brought Eagle into a final, vertical descent. Armstrong knew it was crucial to land without any sideways motion, lest they risk tipping over at touchdown. But now came one more problem: The blast of the descent rocket was kicking up moon dust, sending it rushing outward in all directions and wrapping the landscape in a fast-moving haze. Armstrong fixed his gaze on rocks sticking up through the blowing dust; using them as reference points, he guided Eagle slowly downward, about as fast as an elevator. Words of warning came from Earth: just 60 seconds of fuel left before he would have to abort the landing.

In the back of his mind, Armstrong knew that once they got below 20 feet or so, even if the engine ran out of fuel, in the weaker lunar gravity they would just fall the rest of the way onto the surface and be okay. Now another call from Earth: 30 seconds of fuel left before a mandatory abort. And then, from Aldrin: "contact light." A blue light on the instrument panel signaled that one of three spindly probes at the end of Eagle's landing legs had touched the surface. The craft settled onto the Sea of Tranquility so gently that neither man felt the impact. Armstrong shut down the engine—with about 20 seconds' worth of fuel remaining. Then all was still. Seven hours later he would emerge from Eagle, climb down its ladder, and take the momentous step the world was so excited about.

But for Armstrong himself, the moment of triumph had already come. He keyed his mike and announced, "Houston, Tranquility Base here. The Eagle has landed."