That’s it! The man with the scraggly beard was Mr. Irvin, my algebra teacher from Saratoga High School. We hadn’t seen each other in 17 years, and back then he’d been standing before a chalkboard in a short-sleeved white dress shirt with, if my memory is true, a shirt-pocket protector. Now he was clad in Gore-Tex and Polarfleece, all caked with 2 1/2 weeks of trail dust. But it was definitely the same guy.

How infinitesimal are the odds of bumping into someone you know thousands of miles from home? Well, it’s more likely than you think. My former math teacher was the third acquaintance I’d met in Asia in the span of three weeks. And two of those encounters were, once I thought about them, perfectly explainable.

These seemingly chance meetings happen to me so often I’m no longer surprised by them. Those of us who love to travel are linked by an invisible web of connections that often sends us to the same remote places at the same time. The late photographer Galen Rowell, who experienced many of these encounters, wrote that like-minded people travel down hidden corridors that often converge unexpectedly.

If, for example, your passion is Mozart, or grand cru Bordeaux, or maiden voyages, chances are your travels will one day lead you to Salzburg, or St- Émilion, or the port of Miami. And the odds are good that eventually you’ll bump into a friend there who shares your passion.

In that light, my Nepal reunion with my old algebra teacher was not only foreseeable, it was almost inevitable.

In the 1950s and ’60s, before he settled down to try to teach second- order polynomial equations to bored teenagers, Dick Irvin had been one of America’s top Himalayan mountaineers. We tried to exploit this every chance we could: Our teacher would be handing out an algebra quiz, and we’d plead: “Can’t we take it tomorrow, Mr. Irvin? Tell us about that big storm on Makalu. ” Occasionally he’d fall for it.

But his stories were enthralling, and one day I asked him to recommend a few mountaineering books I could check out from the school library. Toward the end of the school year he took me and a few classmates up to Castle Rock, in the hills above Saratoga, and showed us some knots and climbing moves.

I’m sure Irvin had no idea what he was starting. Mountains took over my life, and I spent the next couple of decades hiking and climbing the great ranges of the world.

If mountains happen to be your passion, you’ll one day make it to Nepal to see the greatest range of them all, and it’s likely you’ll go in the fall, the best season for trekking. And there’s a good chance you’ll one day find yourself in the picturesque village of Ghorepani, which occupies a ridge high above the Kali Gandaki river, astride several of the most popular trekking routes. Which is where I happened to be standing, catching my breath, when Dick Irvin came bounding up the trail.

A few years after I graduated from high school, he’d resigned his teaching post and returned to the mountains, his original love. He took a job with Mountain Travel Sobek, the East Bay adventure travel company, and, at the height of the trekking season, was leading a group on a 21-day circuit around Annapurna. The standard stopping place on Day 18? Ghorepani.

In retrospect, that meeting seemed almost predestined. So did the one a week earlier, when I ran into my old skiing instructor, Mimi Vadasz, outside the Royal Nepal Airlines office in Kathmandu. She was also a climber, en route to Makalu, the same mountain we used to ask Irvin about. In those days, the Royal Nepal office was a reliable place to bump into old mountain friends: Just about everyone had a problem with their reservations.

My third Asian encounter, though, was one of those bolt-out-of-the-blue coincidences. One misty morning on Koh Samui, an island off the east coast of Thailand, I walked down to the beach and bumped into a guy I’d once shared an office with. I can’t think of any connection, any hidden corridor, that would have brought us both to that place at that time.

I’ve had a few other chance meetings like that, and it always makes me wonder how many near-misses we have: The sixth-grade classmate who strolls by while we’re peering into a shop window on the Champs-Elysées, the old girlfriend who strides into an Outback pub half an hour after we’ve left, the former neighbor who strolls down the dock in Ketchikan minutes before our cruise ship ties up. This sort of thing must happen all the time.

There’s another phenomenon that will be familiar to anyone who’s ever spent time on the world-traveler circuit: You’re constantly bumping into backpackers you’ve previously met in distant parts of the world. You have a beer with a Danish guy at a bar near the Blue Mosque in Istanbul, and then you see him again on Kao San Road in Bangkok. You ride the overnight train from Cairo to Aswan with a pair of Irish women, and five months later you bump into them on the Milford Track in New Zealand. These reunions are far from mysterious: The world-traveler circuit really is a circuit, and the young vagabonds on it follow a well-established path.

But it points up one more aspect of travel: The more friends you make, the greater chance you’ll have a delightful reunion with them in some far corner of the globe.

This story originally appeared in the San Francisco Chronicle.