To this day, Bud Grant still can’t answer the question. Neither can Rich Gannon or Bernie Kosar or Jon Gruden, or anyone else on the long list of luminaries who wonder why it took nearly 30 years for Marc Trestman to become a head coach in the NFL.

Trestman used to wonder, too, during 17 seasons as an NFL assistant with eight teams. But long before last January — when the discussion began anew, after he was hired at age 57 to coach the Chicago Bears — the St. Louis Park native had begun to see things in a new light. Fretting about his long wait wasn’t going to get him any closer to his dream job. Instead, Trestman came to believe that each twist in his circuitous career path was molding him into a man worthy of leading an NFL team, sustaining his faith that he would eventually get there.

Armed with that fresh outlook, he stopped worrying about the end and put his mind to the means. Nine years removed from his last NFL job, Trestman has become a more outwardly focused person, guiding the Bears into Sunday’s game against his hometown Vikings with a confident and compassionate hand.

His five-season tenure as a head coach in the Canadian Football League enhanced Trestman’s reputation as an offensive savant known for his way with quarterbacks. That made him an intriguing choice for the offensively challenged Bears and underachieving signal-caller Jay Cutler. Trestman already has earned high praise from his players — and the game ball after a 24-21 victory over Cincinnati in his debut last week.

Some have considered the former Gophers quarterback an unusual fit in Chicago; reed-thin and bespectacled, with a scholarly manner and a self-help author’s vocabulary, he comes off as the anti-Mike Ditka. None of that will matter if Trestman can lead the Bears to the playoffs for the first time since 2010. In that regard, they might be the perfect match: a franchise pining for an unfulfilled ambition, paired with a coach grateful for the chance to realize his own.

“Having looked back at the journey, I think I understand,’’ Trestman said last month, just after the Bears broke camp. “I have a much better perspective on it now than I ever would have had if this had happened 10 or 12 years ago. The wait was very much worthwhile, because all those experiences go into making you the person you are and the coach you are.

“I have complete appreciation for this moment and respect for why it took so long. People say this all the time: If you want to get to where you want to go, just stay focused on what you’re doing, put your heart into it and don’t worry about the returns. This came, really, out of nowhere. But really, it came out of hope and passion.’’

Not to mention persistence.

“I never did understand why he wasn’t hired earlier than this,’’ Grant said. “I’m glad he’s got this opportunity now. He’s certainly paid the price.’’

‘Quarterback whisperer’

Had Trestman listened to Grant, he might be practicing law or selling municipal bonds, rather than roaming Soldier Field. When Grant hired him to coach the Vikings’ running backs in 1985 — the first NFL entry on Trestman’s voluminous résumé — he warned him that coaching is a sure ticket to a vagabond life.

He couldn’t have predicted that Trestman would become the ultimate football nomad. As a young law student at the University of Miami, Trestman convinced Howard Schnellenberger to make him a volunteer assistant in 1981; since then, he has coached for 12 different teams, in two countries, in the CFL, NFL and college. He served as a quarterbacks coach during most of that time, with stints as offensive coordinator for Cleveland, San Francisco, Arizona and Oakland.

Nicknamed “the quarterback whisperer’’ for his extraordinary rapport with players at that position, Trestman has made them the engines of his dynamic, complex and inventive offenses. The Bears’ new, hefty playbook can trace its roots all the way back to St. Louis Park, inside the mind of a boy who dreamed in X’s and O’s.

Trestman’s father, Jerry, owned a restaurant and bar on Chicago Avenue — just blocks from where the Metrodome would later be built — and played in a band. Marc helped out at the restaurant and shared his dad’s love for music and football. When he wasn’t designing plays for neighborhood street games, Marc was scrutinizing the Vikings with Jerry, imitating a coach long before he thought of becoming one.

Trestman played three seasons with the Gophers, backing up quarterback Tony Dungy, and transferred to then Moorhead State for his senior season. His playing career ended when he failed to stick with the Vikings, who twice brought him to training camp as a defensive back. Though Trestman was admitted to the Florida bar in 1983, he left the law behind, parlaying his volunteer job at Miami into a full-time gig as quarterbacks coach.

Two years later — based on Trestman’s work with Kosar, who led Miami to the national championship in 1983 — Grant came calling.

“I remembered what a good athlete he was,’’ said Grant, whose son Mike played against Trestman in high school. “And he was eager to learn.’’

He was not convinced he had found his life’s purpose. After coaching in Tampa Bay and Cleveland, Trestman returned to the Vikings as quarterbacks coach in 1990, then was let go by new coach Dennis Green in 1992. Trestman moved to Florida and sold municipal bonds, figuring he was done with the game.

“I liked what I was doing,’’ Trestman said. “I was focused on my family and on building a business. And then football found me again, with no intention. That’s when I thought, ‘This must be what I’m supposed to do.’’’

San Francisco coach George Seifert revived Trestman’s coaching career in 1995, starting a 10-year run in which Trestman and his quarterbacks flourished. As the 49ers offensive coordinator, he directed the highest-scoring offense in the league and laid the frame work for Jerry Rice to set a then-NFL record with 1,848 receiving yards that season. In Detroit, his instruction helped Scott Mitchell throw for 3,484 yards, then the second-highest total in franchise history. In Oakland, he coached the NFL’s most productive offense and helped Gannon, at age 37, earn honors as the NFL’s Most Valuable Player.

But his second act was no more stable than his first. Though he was lauded for his intellect, his attention to detail and his immersive work ethic, Trestman’s career stalled again in 2006, when his two-season run at North Carolina State ended with the coaching staff’s dismissal.

Disillusioned and angry, Trestman found himself contemplating the footprint he had left through his 51 years. He had spent most of it driven by the tangible measures of his profession: wins and losses, yards and touchdowns. Behind the details, he realized, there were hearts and minds and human beings he never had really seen. In his next job, he vowed not to make the same mistake.

“You start thinking about your mortality, that time is running out and you’ve got to figure this thing out,’’ Trestman said. “What am I going to leave if I’m just focused on me? You start thinking more and more about giving everything of yourself that you can and asking nothing in return.

“That was really a transformation for me, realizing that you’ve got to get first downs, and you’ve got to score, but the fulfillment comes in the relationships built around doing that. The relationships are the purpose. You can help [players] master their craft, and you can help them be better people and fathers and husbands when they’re done.’’

Success Up North

That attitude quickly endeared him to the Bears. Trestman has fostered mutual respect with his players, soliciting their input and giving Cutler the latitude and tools to take command of the offense. Last Sunday, Cutler confidently led the Bears to a come-from-behind victory that left teammates raving about Trestman’s play-calling and faith in his personnel.

“He’s been really receptive to my ideas,’’ Cutler said. “He’s really smart, not only about football, but about life. He wanted to help the guys as much as possible, not only on the field but off.’’

Trestman got a little off-field aid himself on his way back to the NFL. His daughters, Sarahanne and Chloe, had been tugged all over the country by his career; when he took the job at North Carolina State, he promised them they could finish high school in Raleigh, N.C.

Jim Popp, general manager of the CFL’s Montreal Alouettes, had admired him since Trestman coached alongside Popp’s father in Cleveland. To land him as head coach, the Alouettes offered to allow Trestman to live in Raleigh during the offseason and bring his family to Montreal for frequent visits. After leading the team to the CFL’s title game in his first season, Trestman guided it to two championships and built quarterback Anthony Calvillo into a two-time league MVP.

“Marc was never afraid to say ‘I don’t know everything,’ even in public,’’ Popp said. “He wasn’t afraid to take advice and give it a try. And he was always watching, listening and learning, educating himself so he could grow and get better.’’

Though Cutler has a history of fraught relationships with coaches, former Vikings executive Jeff Diamond predicted Trestman will be able to tap his full potential, given Trestman’s interpersonal skills and his association with many of the game’s greatest minds.

“He is going to be a successful head coach in the NFL,’’ said Diamond, a friend of Trestman’s since childhood. “He’s a creative, innovative guy and a great leader who has benefited from all of his life experiences. He should have had this opportunity a long time ago.’’

Trestman’s parents, Jerry and Sharon, and sister Cari all live in the Twin Cities and are adjusting to the idea of rooting for a division rival of their beloved Vikings. Trestman, known for his ability to counter whatever opponents throw at him, is adapting, too.

He acknowledged that Chicago is a big stage for a debut, draped in history and tradition. Still, Trestman said he is not nervous, despite waiting so many years for this moment to arrive. He hadn’t planned on taking the long way, but it turned out to be the best route.

“I think the thing I appreciate most now is that I got this job when I was never thinking about getting it,’’ he said. “I felt as long as I was focused on being the best head coach I could be in Montreal, that somewhere along the line, I would be given genuine consideration. I’m so grateful. And I’m confident that the passion I have for this game is worthy of the opportunity.’’