The two brothers, separated by only 15 months, sat in the back of their father's 1962 Chevy as it pulled up to an elementary school in Iowa City.

John Harbaugh was 8. Jim Harbaugh was 6.

John and Jim grew up in their father's football environment, starting when they were toddlers transported to practice in a stroller by their mother, Jackie.

But at Iowa -- one of the 14 stops made during a coaching career that stretched from Ohio to California -- Jack's job title included chauffeuring his boys to school.

Because his time was limited, Harbaugh made certain it was meaningful.

Just before his sons would reach to open the door, Jack would turn around, scan his audience and deliver the same 20 words.

"OK, men, grab your lunchboxes and attack this day with an enthusiasm unknown to mankind," he'd say.

"And don't take any wooden nickels."

Follow us on Facebook and Twitter to read them first!

Jack Harbaugh can't remember where the saying came from. The wooden nickels line had been passed down from his own father as a reminder not to be taken advantage of.

But it was the first part of his parting instructions that sank in.

"It had a cadence to it and it kind of built and crescendoed," Jim Harbaugh says, his voice raising for emphasis, "OK Men, attack this day with an enthusiasm UNKNOWN TO MANKIND."

They turned out to be words to live by.

"In this world, you can choose to be positive or you can choose to be negative," Jack Harbaugh says. "You can choose to see things through a set of eyes that sees good or you can choose to see things in life that aren’t so good.

"At least every day, they were reminded to look at it through a positive set of eyes. Let the lens of your eyes be positive."

Years later, when Jim Harbaugh was introduced as Stanford's football coach in 2007, he was asked what he brought to the job.

Without pausing, Harbaugh repeated the words told to him by his father.

"I was like, 'Wow,'" Jack Harbaugh says. "It had never been talked about. (Jim) never said, 'Wow -- that was really something I thought about or that's something that's been a part of my life.

"It was just something I always told them."

It was something they remembered.

"That's probably the greatest lesson," Jim Harbaugh says. "If you have health, then one day, imagine what you can accomplish."

***

John and Jim Harbaugh have certainly accomplished a lot. Both are rising NFL head coaching stars -- John with the contending Baltimore Ravens and Jim with the one-loss San Francisco 49ers. And both give plenty of credit to father Jack, who spent 19 years as a head coach at Western Kentucky and Western Michigan. Jack, age 72, still watches his sons' game film every week, getting FedEx packages from Baltimore and San Francisco and taking furious notes on everything he sees. But don't think Jack is still telling his sons what to do. He says the game has "passed me by." He even says he wishes he could somehow go back in time with the benefit of what he's learned from his two boys.

What has never changed, however, is Jack's ability to tell his sons, very clearly, what matters. That's something all great coaches and parents do. It's something both Jim and John will be doing Thursday when their teams meet in an NFL game. And it's something Jack's been doing since John and Jim were old enough to throw a football.

***

The Harbaughs always lived close enough to their father's work to ride their bikes and see their dad. Jack often rose before the sun and spent 12 to 14 hours at the office, leaving Jackie to run the house.

Jack refers to his wife of almost 50 years as the best head coach he has ever worked for. He was the assistant coach while his kids -- John, Jim and daughter Joani -- made up the rest of the team.

But Jackie, a former high school cheerleader and school teacher, ran the show.

Part of Jackie's job, she believed, was to give them a window into their father's life. She wanted her kids to see how Jack interacted with his players. How he was tough, but fair. How he wanted them to be good students and better people. How he wanted them to live up to their full God-given potential.

He wanted his kids to learn about discipline. About being on time and about doing the things the right way.

"That's what you talk to your players about," Jack says. "That's what you’re going to expect from your kids."

Jack was all business in practice, ever mindful his children were watching. But he wanted them to be comfortable, too.

At Michigan, where Jack served as an assistant to Bo Schembechler, Harbaugh got the OK to allow his boys to be around practice. They'd stack tackling dummies, help clean up, and even got to spend time with players inside the locker room.

But just like in the Harbaugh household, if rules were broken, there would be consequences.

"You lived with knowing that at any time they could do something and they were going to get snapped at," Jack says.

During one drill, Jack was watching the defense while Schembechler ran the offense. Without warning, a ball sailed over Jack's shoulder and onto the field. Jack cringed.

"I said, 'Please don't let that be one of my kids,'" Jack says.

When one of Jack's sons ran onto the field to retrieve the ball, Schembechler stopped practice.

"Get those kids off the field," Schembechler growled in his slow and steady cadence.

But Jack's sons stayed, and they saw the way their father worked. They saw the way players listened.

They also saw how he dealt with failure.

Throughout his coaching career, Jack's life was a roller coaster. He was fired from his head coaching job at Western Michigan in 1986. He was on a Michigan staff that lost three Rose Bowls in the seven years he worked for Schembechler. His Western Kentucky program endured crippling budget cuts even though the Hilltoppers won the 1-AA national championship nine years ago.

In every instance, good or bad, Jack wanted his kids to learn how to deal with life.

But he wanted them to learn for themselves, living by words he once heard from Ohio State coach Woody Hayes:

Don't do for your kids what they can do for themselves.

"That's the way we kind of looked at it," Jack says. "We didn't understand what it meant at the time but let them do for themselves what they’re capable of without trying to mask things or sugarcoat things or make it look better.

Jack told his kids that life wasn't about what happened, but how you dealt with it. That, he believed, defined you as a person.

"You want them to be competitive -- I want them to understand that everyday is a fistfight in life," Jack says. "You’ve got to battle and you're going to get knocked on your can, but you’re going to get back up if you're competitive."

It's a side of Jim that Jack and Jackie saw earlier this season after a 49ers victory in Detroit.

After the final seconds ran off the clock, Jim celebrated with his players, sprinting across the field to meet Lions coach Jim Schwartz. Harbaugh delivered a forceful handshake and slapped Schwartz on the back.

Words were exchanged.

Jack and Jackie watched the whole thing unfold on television back in Milwaukee.

Jackie smiled. That was a passion unknown to mankind, for sure.

Jack understood the moment as well, but knew that in a media environment much different than the one he coached in, his son would take some heat.

But he loved his son's competitive enthusiasm.

"You've got to be yourself and if you're not, you're a phony," Jack says. "It comes shining through if you're not careful."

***

Loyalty has always been a bedrock of Jack Harbaugh's make-up.

Jack always made one thing perfectly clear: If you need something, Jackie and I will always be here for you. That bled through his entire coaching staff and down to the players.

Michigan coach Brady Hoke learned the lesson first-hand.

Working on Harbaugh's Western Michigan staff, Hoke was sent to Fort Wayne, Ind., to finalize the recruitment of a quarterback Harbaugh wanted to sign. In an era where home visits were critical in building relationships, Harbaugh had sent his assistants out to oversee the signing of every recruit's national letters of intent.

Hoke left Kalamazoo on Valentine's Day, intending to make the short drive to Fort Wayne and return home.

Instead, Hoke encountered a blizzard that had paralyzed Fort Wayne, closing the city's schools. As conditions worsened, the young assistant coach found a pay phone to inform the recruit's mother he had run into trouble.

The response he got wasn't one he expected.

"Have you talked to Jack Harbaugh?" the mother asked.

No, he hadn’t.

"You need to talk to Jack Harbaugh," she replied, giving Hoke a telephone number he didn't recognize.

Turned out Hoke's wife, Laura, was in labor -- three months early.

Harbaugh rushed to University Hospital in Kalamazoo and sat in the waiting room with Brady's and Laura's mothers.

"Jack Harbaugh took charge," Hoke says. "But that's just the person he is. He's tough, but he had a great personal side to him."

Kelly Hoke was born that night, weighing 1 pound, 14 ounces. With Hoke stranded in Fort Wayne, Harbaugh was one of the first people to see Kelly.

"You could hold her in the palm of your hand and her little hands and arms were hanging down," Harbaugh remembers.

For the next 19 years, whenever Valentine's Day rolled around, Jack Harbaugh placed a call to Kelly Hoke, wishing her a Happy Birthday.

Hoke never forgot it.

"You felt such a loyalty to him you wanted to make sure you coaching your tail off for him just because of how he and Jackie treated you as a couple," Hoke says. "You always felt close to them."

***

The phone conversations between father and sons take place on a regular basis.

Rarely, if ever, do they revolve around football. And haven't this week, either.

Jack and Jackie Harbaugh have lived the coach's life enough to understand what game week entails and about the challenges each day bring.

Jack never places a call, never forces his opinion where it’s not wanted.

That carries over to the film sessions in his basement in the days leading up to each game.

Jack limits his film reviews to minimum details, limiting them to the notepad that sits on the chair-side table. He stops and starts the video, taking notice of the movements of the offensive and defensive linemen, gifted enough to know what’s coming next.

He pauses the video from a 49ers-Giants game when his son's team is about to run a play on third down and short.

"This is a situation when Bo (Schembechler) used to say, 'It's time to grind the meat,'" Harbaugh explains.

He lets the play run before stopping it again with his coach's clicker.

"They didn't grind it very well, did they?," he asks the reporter sitting next to him.

Most observations stay in the basement.

On the off-chance John or Jim inquire about what he's seen on that week's coaches cuts, Jack passes his observations on, preferring to keep the conversations about family and other topics.

But even when the conversations include football, there's routinely a lesson imparted.

"Pretty much everything I learned, I learned from my dad," John Harbaugh says. "You get a chance to talk to him after games and you put it in perspective in terms of remembering what’s important."

There are times, Jim Harbaugh acknowledges, when Jack's expertise is required even though Jack prefers to stay out of his son's business.

"Any time I've got a problem or an issue or a decision that's really tough, all I’ve got to do is call him," Jim Harbaugh says. "Something that would take me three hours and give me a massive headache, I just ask him and 30 seconds later, I've got the perfect solution."

Jack always makes sure any decision comes not from what he thinks is right, but what his sons know is.

Last winter, when Jim Harbaugh pondered leaving Stanford, he called his father. The options seemed endless. Harbaugh's name headlined several prominent job openings, including at his alma mater at Michigan along with NFL vacancies in Miami, Carolina and San Francisco.

Harbaugh called his father in Wisconsin, seeking guidance.

Jack was careful not to overstep his boundaries.

As they discussed Jim's options, the son kept asking his father what to do. Jack told him what he thought didn't matter. Jim kept pressing.

Again, Jack told him he had to make up his own mind.

Finally, Jim snapped.

"Damn it, I called you because I want your opinion," Jim told his father. "Just give me your opinion. I'm not telling you I'm going to go that way and if I don't want to go that way, I won't go that way.

"But I called you because you're my dad and I want an opinion."

Jack smiled.

He had always encouraged his children to speak their minds.

"I took that as one of the great complements," Jack says. "Every once in a while, you have to express yourself and you have to be who you are."

But Jack didn't relent. Jim had to decide on his own.

***

The expectation growing up in the Harbaugh home wasn’t for the sons to follow in their father’s footsteps.

Jack and Jackie Harbaugh simply wanted their children to be happy.

He gave them simple advice: Don't lie. Don't cheat. Don't steal. Those were game-changers and would lead to compromised relationships.

While Jack preached enthusiasm for each new day, he didn't look too far ahead. Coaches simply can't afford to.

"You never think about what life's going to be like five years down the road or 10 -- you just go though the day and try to make good decisions," Jack says. "Sometimes you do, sometimes you don't. You just hope this day will be a good day.

"Pretty soon it's a week, then it's a month, then it's a year -- then it's way down the road."

Joani, born five years after Jim, also spent time with her father, learning to hot-splice game film by the age of 10. She would fall in love with a coach, marrying Indiana basketball coach Tom Crean while he was an assistant at Western Kentucky. She was selfless, but every bit the leader her brothers are. She just wasn't a leader who appeared on TV.

John played defensive back at Miami (Ohio) while Jim became a star quarterback at Michigan before moving onto the NFL.

Did they compete with each other? You bet. There's a great family story about how the boys each tried to throw a football over a tree. And not just any old tree -- a towering Colorado spruce. Jim, always taller, tried and tried until he could finally do it. John, never quite as good an athlete, could not. The elder brother was always quieter, but he burned just as hot inside. That's how he got to the NFL.

John watched practice at Michigan and paid close attention to the way Schembechler ran his program.

"You can't have a better childhood," John Harbaugh said when he landed his first NFL head coaching job with the Ravens. "When you grow up in that environment, part of your life values and the things you learn are three important things.

"No. 1 is the team. The second important thing is the team. The third most important thing was the team. That's what it's all about."

When Jim was introduced in San Francisco, Jack visited the 49ers facilities and saw six words boldly painted on the wall.

The Team, The Team, The Team.

After a Thanksgiving meal one year, when Jack and Jackie visited Baltimore, John informed his family they were going for a ride. They traveled to a downtown homeless shelter where the Harbaughs served meals to the less fortunate. There were no television crews around, no reporters -- just the coach of the Baltimore Ravens and his family.

Earlier this year, when the 49ers visited Washington to play the Redskins, Jim took his team to Arlington National Cemetery. There, Harbaugh took his players to the Tomb of the Unknown Soldier, telling a story about loyalty and sacrifice -- two staples of the lessons Jack and Jackie Harbaugh passed on to their sons.

"You ask me what my dad means to me," Jim Harbaugh says. "He took me to ballgames. He played catch with me. He believed in me.

"My whole life, even from a young age, making my dad proud of me has been really important to me. I hope I never grow out of that."

***

On Thursday, Jack and Jackie Harbaugh will travel to M&T Bank Stadium in Baltimore, where John’s Ravens will face Jim's 49ers.

A day earlier, they will visit their oldest son at practice before attending the 49ers' walk-through.

While the Thanksgiving night game will bring family members from around the country, Jack and Jackie won't stay for the game. They will pose for a family photo on the field long before kickoff, reuniting their three children for the first time in three years.

Then, Jack and Jackie will retreat to John's suburban home to avoid becoming part of the focus.

Jack still doesn't know what Thursday night will be like. It will be an emotional scene, but he doesn’t know what kind of emotions he'll feel as kickoff approaches.

Jim Harbaugh expects the night to be a blend of joy and pain for his father.

Greg Mattison, who worked as Jack Harbaugh's defensive coordinator at Western Michigan and as John Harbaugh's defensive coordinator with the Ravens, expects the night won't be easy.

Not by a long shot.

"It's going to be really hard," says Mattison, now the defensive coordinator at Michigan. "I've seen him up close and the pride he had and how emotional he got after we won a big game.

"Now, he's got two of them and one of the people he loves and one of the people he brought into this profession isn't going to be successful in that game."

Despite that, Jack Harbaugh insists Thursday night won't be about him. It's part of the reason he and Jackie will watch the game in solitude.

"They're going to look across the field and see that guy they grew up with and they were raised with and that’s going to be interesting," Jack says. "But once the ball is teed up, it's a three-hour game and you're trying desperately for your team to win the game."

The Ravens-49ers game has changed the way he communicates with his sons. When Jim was at Stanford, he mentioned nuances John was running with the Ravens.

That all ended when Jim was introduced as the 49ers coach. On the occasions he has met with his sons' coaching staffs, assistants have jokingly reminded colleagues to watch what they say, knowing Jack remains in contact with his other coaching son.

Many aspects of this game week will be different than any other. But in some respects, the routine will remain the same.

As always, Jackie Harbaugh will call both of her sons the night before a game. It's her way of letting them know that she’s thinking of them.

Her message, like any other week, will remain the same with John and with Jim.

Good luck, we're supporting you and we’re pulling for you.

"I can't root for one or the other," Jackie says. "If it would end in a tie, I would be the happiest person in the world."

After the game is over, the families will come together and share a meal, thankful for all they have been given.

Then they will celebrate another major accomplishment. Friday is Jack and Jackie's 50th wedding anniversary.

"We all have a lot to be thankful for," Jackie says.

And a lot to be proud of.

-- Jeff Arnold can be reached at jeffarnold24@gmail.com or follow him on Twitter @jeff_arnold24.

Popular Stories On ThePostGame:
-- 12 Marathons For 2012
-- The Cost Of Extreme Sports
-- Video: Dad Is Red Sox Fan Who Won't Let His Son Root For The Yankees
-- College Basketball's Dad-Son Coach-Player Duos

The Rock Thanks The Iron Sheik