The thing is this: Once you’ve run a marathon and you realize the distance is a challenge you love, you will try to run another one. And once you’ve run another one, and another one after that, your thoughts will turn eventually, inevitably, to Boston.

The Boston Marathon has long been the Holy Grail for marathoners — for its history and its course, with its leafy suburban start in Hopkinton, past the ululating students at Wellesley, the push up the heartbreaking Newton Hills, the closing miles through Kenmore Square and an uplifting finish down Boylston Street, scene of last year’s tragic bombings.

For runners, it’s Indy. It’s Churchill Downs. It’s Augusta National.

But one of the more special parts about Boston, aside from crossing the finish line, is getting to the start in the first place. That’s because to run Boston you must earn Boston; it’s not a matter of lucking out in a lottery sweepstakes to gain entry. You need a qualifying time tied to your age group from a recent marathon. And that takes something else.

Unless you’re young and naturally gifted, it takes training, and lots of it. But I can tell you that if a late-starting plodder like me can do it — I ran my first marathon at age 42, Boston at 49 — almost anyone can.

I had run a few marathons, falling-apart sloppy, before I fixed on proper training. With some coaching, weekly speed work on a track, and many miles on the Silver Comet Trail, my times improved enough for me to at least think about qualifying.

That said, it took a special alignment of prep work, good weather and one of the great flat courses you’ll find — Columbus, Ohio — to reach my goal one morning in October 2004.

To qualify for Boston back then, I required “a 3:30” — a three hour, 30-minute finish. I trained for four months. Nevertheless, I will never forget the gassed feeling I had at mile 20 in Columbus as I started to “hit the wall,” already pressing. And stressing.

Struggling to relax, I vowed not to look at my watch for the last six miles and 385 yards. I simply would trust my training and my pace, and do my best.

If I didn’t make 3:30, no big deal. There was always another race.

I remember shunning the horizon and staring at my Nikes, putting one foot in front of another. When I crossed the finish line, I blindly clicked my timer off, then looked at my watch:

It read 3:30:14. I needed only to finish before 3:31 in order to qualify.

I made it by 46 seconds. My ticket to Boston. One of life’s hallelujah moments.