Dismay.

This has been especially true in the Asian-American community, where Kim, the son of South Korean immigrants, has been simultaneously lauded as a hero—and feared, only half-jokingly, as “every Asian kid’s worst nightmare.”

The worry: No matter what they achieve, their high-demanding immigrant parents will say Jonny Kim already did that—only better. “We accomplished all this stuff, but really, it’s what he did that matters,” Chu said.

Kim became an internet meme among Asian Americans, who frequently take to social media to express gratitude that he’s not a relative. NASA’s social-media posts about Kim are flooded with comments expressing similar sentiments. “As a fellow Asian, I hope my parents do not get to read this. But, safe journey my man,” one wrote.

Chu wrote about that feeling of inadequacy in a viral post, which inadvertently hammered in the point by containing a typo.

Kim never set out to achieve this trifecta of lifetime achievements. His power, he said, is focus.

“I had no aspirations to be a physician, an astronaut,” Kim said on the Jocko Podcast in 2020. “That’s really important to me even to this day, that you have one singular goal, because you should be all-in on what you’re doing. You should be genuine in what you’re doing, not have some social-climbing, some professional ladder.”

In his telling, it happened because of a series of accidents that included an Ultimate Frisbee injury, a college job doling out parking tickets and a memorization hack that helped him get through medical school.

It all started with trauma during his childhood in Los Angeles. Kim said he witnessed his father, who he described as alcoholic and abusive, pull a gun on their family. Police shot his father dead in their attic.

His desire to physically protect his mother and brother led him to become a Navy SEAL. But an Ultimate Frisbee ankle injury delayed his plan to join the Navy as an operations specialist. When he recovered, a recruiter steered him toward becoming a medic.

In 2005, Kim joined SEAL Team Three, serving as a medic and sniper, among other roles. He earned a Silver Star and a Bronze Star for treating wounded comrades during two tours in Iraq, an experience that motivated him to attend medical school.

But first was college at the University of San Diego. Despite scholarships, he needed a job to take care of tuition. So he handed out parking tickets. “Never think you’re too good for any job,” he said on the Jocko podcast, saying that the gig taught him to stay humble.

Then came Harvard Medical School, where he juggled studies, fatherhood, and exercise on a 3:30 a.m. wake-up schedule. He sought time hacks, he said on the “Stories Behind the Scrubs” podcast, and found one called spaced-repetition learning.

Using electronic flashcards, he graded each card from 1 (had no clue) to 5 (easy answer). In the next session, the system showed him cards at varying frequencies that would optimize learning. “There are small things you can do to enhance your memory retention,” he said.

While studying medicine, Kim met Scott Parazynski, a physician-turned-astronaut, and asked about a career in space. Impressed by Kim’s skills, intellect and poise, Parazynski said Kim would be a strong candidate to become an astronaut.

Kim never dreamed of space as a child. But he liked the idea of inspiring the next generation. He applied to the National Aeronautics and Space Administration’s astronaut program and, naturally, got accepted the first time.

“He really is superhuman,” Parazynski said. “He’s the world’s most interesting man, the Dos Equis guy, in real life.”

As part of what NASA calls the Artemis Generation, Kim is a candidate for the agency’s Artemis missions to the moon and potentially Mars.

At astronaut graduation in Houston, Sen. Ted Cruz (R., Texas) quipped that it was ridiculous that Kim was already a Navy SEAL and a Harvard-trained doctor. “He can kill you and then bring you back to life,” Cruz said, “and do it all in space.”

It was around this time that he became the Asian-American community’s living legend—and source of slight existential dread.

“He’s a Navy SEAL. That’s badass. He’s a doctor, which is every Asian mom’s dream. Now he’s an astronaut, which is every kid’s dream,” said Chu. “We, as Asian Americans, are fans of Jonny out of pride, but also a little bit out of fear. He’s scored, like, 140% on the life test.”

After astronaut graduation, Kim wanted to maximize his potential, so he cross-trained with the Navy and became a certified pilot. But as he prepared for his first space mission, there was one last hurdle.

He is set to blast off on Tuesday in a Soyuz capsule, hitching a ride to the International Space Station with two Russian cosmonauts. In a recent news conference from Star City, Russia, he was asked about the biggest challenge of his mission.

Kim referred to the months he spent acquiring one more skill, because his journey to space won’t be conducted in English. “The hardest part was certainly learning Russian,” he said.

Write to Stu Woo at Stu.Woo@wsj.com