I WASN'T GOING TO MAKE IT. I was almost 16 miles into the New York City Marathon, and there were still more than ten to go. It was my first marathon, and I had the distinct sense that I'd run the first half of the race too fast. Now, my punishment was to drown, miserably, in my own lactic acid.

I crested the steep Queensboro Bridge with a small pack of runners, and as we descended into Manhattan, the ramp swooped sharply to the left toward First Avenue. A few hundred spectators were standing behind the hay bales and police barricades at the bottom of the turn. For some reason, I lifted my arms above my head. Nothing happened. Then a cheer went up. I pumped my fist. It became a roar.

I have never felt a second wind like the one that hit me at that moment. I surged forward, filled with energy, leaving the group behind me, catching the next one, and the one after that.That's the power of the marathon especially New York, which boasts the largest and most international field, has the biggest (and rowdiest) crowds, and, unlike Boston, is open to everyone, fast or slow. For the 2009 event, there were 2.5 million people in Gotham's streets watching 44,177 strangers parade along through their solitary, elective hells. They cheered with the same zeal for friends, for costumed runners, for anyone with their name on their shirt, for no one in particular. I remember a young girl in Brooklyn waving a handmade sign that said, simply, YOU'RE AWESOME RUNNERS!

As the 43,660 finishers that day can attest, almost anyone can run a mara­thon old people, chubby people, Bob from accounting. "It's ordinary people doing ordinary training so they can then do something extraordinary," says Frank Shorter, American gold medalist at the 1972 Olympics and 1976 NYC runner-up. But there is no easy way to the finish line. No matter how much pasta you eat the night before, the body can only store so much energy in its muscles, and for many runners, it's just about gone by mile 20 where they hit the proverbial wall. Whether you're 2009 New York winner Meb Keflezighi, who finished in 2:09:15, or 88-year-old Peter Harangozo, who completed the race after dark in a little under eight hours, going all the way means digging into your deepest reserves.

And yet, training for a marathon is actually easier than you think. You don't even need to give up your other weekend sports and activities. To become a marathoner, you just have to become a runner. The race is merely the celebration of how healthy you've gotten as a result.In the months leading up to the race, my legs turned into small tree trunks andI dropped every spare calorie of fat. The rest of my life seemed to follow. Because I had to be well fueled, I could no longer skip lunch on a busy day. Because I had to spend an extra hour or three each day running, I became far more efficient at work. I got eight hours of sleep because my body demanded it.

Finishing those last six miles of the NYC Marathon was the hardest thing I've ever done. When I finally made it, it took me an hour before I was strong enough to stagger out of the medical tent, wrapped in that foil cape with a zinc medal around my neck, and shuffle stiffly toward my hotel. But as I've come to understand, running a marathon is much more than an athletic achievement. I can now approach any daunting task as something to be broken into steps. And I'm always ready to reach for what I found at mile 20.

"Almost everyone hunkers down and finds a way to get to that finish line," offers former Olympian and longtime coach Jeff Galloway. "You learn to rely on that ability to gut it out not just for running, but for life."

Sign up for an interactive training plan for the NYC Marathon in the Outside Fitness Center.