I'm often asked, "What motivated you to start The Motley Fool?"

The first answer is simple: the chance to work full-time with my brother. But the second, I've never shared.

That answer begins 25 years ago on a muddy field, in Groton, Mass., in the driving rain. A few dozen high-school athletes are slogging to the end of a football practice, and our coach, Jake Congleton, is howling at us. "The season starts in a week! You're not ready! This is not good enough!"

Not good enough, is all I can think, as the coaches leave the field and we huddle the Groton School varsity team in the endzone.

Growing up, there wasn't anything I loved more than playing tackle football. I fought to keep up with my older brother, David, and his friends. Some of them were twice my size. I threw everything I had at their knees to try to bring them down. I dove for catches in our backyard, even when the odds favored landing on the brickwork that marked out-of-bounds. I dealt with fumbles, missing tackles, and losing most days. I got up from one ferocious hit after another, wondering whether my ribs or shoulders or brains were indefinitely out of place. (Sometimes I still wonder.)

Nothing stopped our games, though. We played in the mud. We played in the swampy summer heat of Washington, D.C. We played with frozen eyebrows through ice storms and the driving snow. We played when it was too dark to see the ball. We played through open wounds, bruises, cursing, cheap shots, late hits, delivery sacks, gang tackles, tears, and endless laughter. Football was more important to me than exams, grades, school applications. Not that it should've been, but it was. It was almost as important to me as my high-school girlfriend, Amy.

I expect many of you have loved the game of football -- or any game -- this much. Maybe the game of beating your best marathon time, or the game of ping pong, or basketball. The game of gymnastics, soccer, rugby. The game of anything that drives you with relentless passion toward mastery. My passion was football.

So, there I was, a senior in high school. Co-captain, standing ankle-deep in muck alongside maybe the greatest player in Groton's history, Dave Archer. Our coaches Congleton, Choate, and Alexander had warned us and left the field. So we brought our team together there and agreed -- this is not good enough. Our efforts weren't good enough. Our playbook mastery, not good enough. Our form tackling wasn't good enough. Our line blocking, not good enough.

Everything was just not good enough.

So at dusk, in the rain, we made a commitment that our coaches tried to shut down when they heard it. But we made it because it was essential and authentic. If our linebacker Sean Delaney was going to play with a back injury all year ... if Gat Caperton and others were going to hold down the offensive line with not a hint of glory the whole damn season ... if Chip McDonald was going to have to take some blindside hits as quarterback ... if we were going to put in all the hours, run all the sprints, take all the beatings, and all the heat, and risk all the injuries, then it was simple: Anything less than an undefeated football season would be failure.

That commitment and fierce desire frames the second answer to why I started The Motley Fool with my brother 17 years ago. Those feelings from the football field inform every important decision I've made at our company. They've helped me through the dramatic turns of our business. And they've guided my investments, too, as I've scoured the markets for companies that have the passion, will, commitment and that make sacrifices equal to ours on the high school football field.

The 1985 Groton School Varsity Football Team has led me to businesses like Netflix (Nasdaq: NFLX) and Middleby (Nasdaq: MIDD) and Dolby Systems (NYSE: DLB), each of which has risen many times in value. For the same reason, I've rallied around Berkshire Hathaway (NYSE: BRK-B), Whole Foods (Nasdaq: WFMI), and Costco (Nasdaq: COST).

These companies and their leaders know that the greatest commitments are the ones made when you are all in. The greatest days are the ones spent pursuing mastery, through the muck if you must. And the greatest rewards come when you get the best people united around a common goal, defined by something they truly love.

We finished our season undefeated and untied, for what stands today as only one of three undefeated teams in the past 40 years of Groton football. In our final game, against century-old rival St. Marks, we led 35-0 at halftime, having shaved our heads the day before (an act with permanent consequences for me).

This weekend, we'll be celebrating the 25th anniversary of that season. And you can see my love for it all in this 17-second video, in which Josh Karch throws a 50-yard halfback option pass to me in our hard-fought opening-day win. My post-catch reaction in our jailbird uniforms tells the story: