In 1961, President John F. Kennedy stunned the country by promising that America would land men on the Moon and return them safely by the end of the decade. That announcement came as a surprise to many at NASA; the space agency was just three years old and had little idea about how it would accomplish such a complex and challenging feat, and especially so quickly. One thing NASA did have was seven astronauts, all of them test pilots, and in the next few years the agency would add several more, many of whom would become part of the Apollo program that would set out to keep Kennedy’s promise.

These astronauts were not randomly selected. Most came from the ranks of test and fighter pilots, and had already proven in their military careers that they had the requisite courage and daring to press cutting-edge flying machines to their operational limits. And they all believed, even when Kennedy’s promise seemed most impossible, that NASA would make it possible for them to walk on the Moon before 1970.

In my new book, ROCKET MEN, I chronicle one of the most incredible and undertold stories in American history – the Apollo 8 mission, launched just a few days before Christmas in 1968. Apollo 8 was mankind’s first journey to the Moon, and remains perhaps the most daring mission NASA ever ran. Apollo 8 had it all: an existential enemy (the Soviets), a race against time that came down to the final hours, breathtaking danger and risk, and an incredible finish, all at the end of one of America’s most divisive and fractious years – 1968.

In researching this story, I spent several days with the crew of Apollo 8 – Frank Borman, Jim Lovell, and Bill Anders – and interviewed many more Apollo astronauts. I found that several of these men shared a common style of thinking on certain matters, one that informed their approach not just to their jobs but to their lives. Listed below are six ways I noticed to think in ways that allowed astronauts to do things no humans had done before.

1. It won’t happen to me because I’m better

Frank Borman spent his pre-NASA years as a test and fighter pilot for the United States Air Force. Whenever word spread around his base that a fellow pilot had been killed in training, Frank’s wife, Susan, became devastated, fearing Frank might be next. Frank, on the other hand, reacted as he always did, by thinking, “It’ll never happen to me because I’m better.” Frank knew that kind of thinking was a defense mechanism; he knew it might not even be true. But he believed himself best nonetheless, and soon enough it became true. NASA picked him for its second group of astronauts, then put him in command of Gemini 7, a two-week orbit of Earth. Three years later, the agency chose him to command Apollo 8, mankind’s first journey to the Moon.

2. Push things to their limits – and beyond

As former test and fighter pilots, Apollo astronauts had years of experience pushing aircraft up against – and even past – their operational limits. The risks were immense – many of these men had watched their fellow pilots in the military die in cutting-edge aircraft. But it never occurred to them to stop; there was simply no other way to know the true potential of a machine – or of oneself – without pressing into places others thought impossible. And this instinct didn’t end in airplanes or even in rockets. Many Apollo-era astronauts drove high-performance sportscars, especially Corvettes, the kinds that could testify on a moment’s notice as to what automobiles could do if pressed into a new kind of red.

3. I’m not turning back

About 80,000 miles into Apollo 8’s trip to the Moon, commander Frank Borman became ill, a surprise to his crewmates and to NASA, since Borman had never been sick during any of his flights as a test pilot, fighter pilot, or astronaut. As Borman vomited and experienced diarrhea, crewmate Bill Anders thought it best to radio Houston and report on Borman’s illness. As commander, Borman vetoed the idea – if NASA found out he was sick, meddling doctors might order the flight terminated and order Apollo 8 back home, and Borman wasn’t about to risk that. As he began to improve, a compromise was struck – Anders would send a private message that only NASA, not the public, could hear, reporting on Borman’s condition and seeking a possible treatment. When NASA brass heard it, they seriously considered ending the Apollo 8 mission. It never came to that, but Borman’s son, Fred, had an opinion about what would have happened if Apollo 8 had been ordered home. “Even if my dad had suffered a heart attack and was lying paralyzed in the spacecraft, he would have ordered his crewmates to continue the mission. That was my dad.”

4. Move on from failures – fast

Most astronauts from the Mercury, Gemini, and Apollo eras were selected from among America’s finest test and fighter pilots. In addition to brilliant flying skills, these men often seemed to possess another, more ethereal quality – they didn’t dwell much on failure. That must have been a nice benefit to NASA, as space flight was new and unlikely to be perfect. And it was proved out soon enough when Apollo 1 astronauts Gus Grissom, Ed White, and Roger Chaffee perished in a fire on the launch pad during a training exercise. The accident devastated astronauts and NASA management, and for a time it put the brakes on the American space program. But it didn’t change the outlook of many. Frank Borman told Congress, which was investigating the accident, “Let’s stop the witch hunt and get on with it.” And Apollo 14 astronaut Edgar Mitchell summed it up for many astronauts when he later said, “It wasn’t surprising that there were accidents like on Apollo 1 – those were just the hazards of exploration, as we saw it. We went ahead anyway, because that was the name of the game.”

5. Learn how to die in order to live

Apollo astronauts trained relentlessly in a command module simulator, an Earth-based model of the Apollo spacecraft they would take to the Moon. The machines were highly accurate mock-ups of the real thing, their cabins outfitted with working versions of every switch, lever, dial, and readout the astronauts would use on their lunar journey. Leading a team of instructors was the Simulation Supervisor, or SimSup. Again and again, the SimSup would unleash an arsenal of emergencies, failures, malfunctions, and conflicts into the simulation, the more catastrophic the better. Often, the crew “died” trying to work its way out of these situations. But the training continued, until repetition began to groove instinct into the astronauts and ground crew alike, and dying helped the men learn to survive.

6. Be willing to switch perspectives

The Apollo missions didn’t just take the first human beings to the Moon, they also gave those humans a perspective on Earth no one before had been privileged to experience. “We see the Earth now, almost as a disk,” radioed Frank Borman to Houston, as Apollo 8 moved away at nearly 20,000 miles per hour. Until then, astronauts had never seen Earth as a whole. Not long after, Earth appeared about the size of a softball to the Apollo 8 crew. It was then that things started looking odd to Bill Anders – thinks weren’t where they were supposed to be, shapes didn’t belong. And then it hit him – there was no up or down in space, or even in the universe. Just because the globes in his grade school classrooms showed Antarctica at Earth’s bottom didn’t mean it would look that way from space. Turning himself upside down, he now understood the continents, the hemispheres, and the shape of a world he’d seen only one way until now.

For more on the Apollo 8 mission and how astronauts think, check out my new book Rocket Men: The Daring Odyssey of Apollo 8 and the Astronauts Who Made Man’s First Journey to the Moon