Sometimes it takes someone else to show us how much of a difference we make in people’s lives. For Johnny Jameson, a Los Angeles letter carrier, that someone lived in an apartment where he delivered mail.

“I didn’t know that my life had such an impact,” he says. The man in the apartment was a film director and the movie he produced about Jameson’s life is now touring the country.

Jameson and the film came to town in January, part of MountainFilm on Tour Savannah, where thousands of school kids and other movie-goers watched his inspirational story.

How many of them left the theater with the same reaction that Jameson had when he first saw his life on film, in Vincent DeLuca’s “Mile 19?” “I was just mind-blown,” he says.

The documentary starts in 1984, when Jameson co-wrote a song for the Los Angeles Olympics. “It went viral,” he says. “All the TV and radio stations played it constantly.”

The song, “Olympic City,” made Jameson, a part-time singer, part of the games. So when L.A.’s mayor announced an Olympics-funded marathon in 1986, he felt moved to run.

Or walk. Or walk backwards! “In L.A., man, it’s just a joyful place to be,” he says of that first marathon. “You’re inspired to do all kinds of crazy stuff.” He finished in last place.

Jameson finished the marathon the next year (running forward), the next year and the next. Once, he dribbled a basketball while running. Once, memorably, his co-workers ran with him.

He’s now run the L.A. marathon for 31 years. He’s become what they call a “legacy runner,” one of about 140 “originals” who just keep on running – out of sheer defiance.

“We started meeting each other,” he says. “We formed this bond and say, ‘Hey, let’s continue to do it as long as we can still do it. I’ve been rolling with the group ever since.”

I imagine every one of those 140 “legacy runners” has a story about how they started and why they still do it. Just as I have a story about how I started in radio and why I still do it.

And, just to be as explicit as I can about it, just as everybody watching that film and you, too, reading this, can know that it’s possible to finish, endure and overcome obstacles.

“When you hit mile 19 in a marathon, you’re going to feel bad,” he says. “Man, I felt so awful at mile 19 and I just had to dig in because I wanted to keep my legacy status.”

Once you quit something, it’s harder to get back in. That doesn’t mean you can’t rebound from failure. But as a saying goes, it’s better to wear out than to rust out. Jameson agrees.

“What we got to go through in our every day lives, it’s just a grind, man,” he says. “And a grind can be joyful… The game is to just hang in there and grind that bad boy out.”

Grinding out saves us from demons. In Jameson’s case, he came back from Vietnam with flashbacks and bad dreams. He’s better now. But Fourth of July fireworks still rattle him.

“It’s good therapy,” he says of running. “Just try to shed off some of that baggage that you’ve been carrying all your life that you really don’t need anymore. Just shed it.”

You don’t need a film to come along and show you your potential. Find your inner film director. Take a legacy runner along with you in your mind. And you can finish the race.

That’s how a graceful and humorous Los Angels postal service worker, an unsung hero, perhaps sorting mail at this very moment, has had an impact on people across the nation.

His story was brought to our city by MountainFilm on Tour Savannah, which screens inspiring and educational films that celebrate triumphs in human society and in nature.