When it comes to travel, my husband and I are planners: Before every trip we peruse a stack of guide books from the library, study some history, and map out our logistics.

Although we still leave room for serendipity, planning helps us make sure we don’t miss an interesting event — or accidentally land in the middle of one. Like the Paris Marathon, for instance.

But in spite of our best planning efforts, our many years of traveling together have taught us an inescapable truth: At some point the trip you planned will become the trip you’re on.

You’ll wake up covered in bedbugs. You’ll get off the train at the Basel Bad Bf station instead of Basel SBB (big difference). Or maybe you’ll be stranded for 14 hours at Rome’s Fiumicino airport as Vueling concocts ever-more-creative excuses for your delayed flight.

The point is that things won’t go according to plan — and there won’t be a damned thing you can do about it. And at that point you’ll have a choice: Will you fume in anger at your ruined trip? Or will you roll with it, and see where this new adventure leads?

Our last trip tested this philosophy. Five days before our flight home, I noted that the stairs outside our ancient apartment were slippery from the night’s condensation, and thus paid meticulous attention to each of the 89 steps.

Finally — on the 90^th and last step — I relaxed. “I made it!” I thought. That’s when my leg slipped out from under me and I fell backward onto the stone staircase.

I heard the “whump” before I felt the searing pain in my back. Instinctively, I crawled around on all fours for a couple of minutes and tried to catch my breath. Then I climbed back up to the apartment. “I need a doctor,” I told my husband.

It turned out I needed a hospital.

Luckily, the scans didn’t spot any broken bones or damaged discs. “Nevertheless, these soft-tissue things can be surprisingly painful,” said the doctor, “but it’s important to keep moving as much as possible.” I nodded while I mentally hollered obscenities.

Back at the apartment I was heartbroken as I iced my back and listened to life go on outside. “Those people have no idea how lucky they are to be ambulatory,” I thought. To pass the time I read several books and snapped iPhotos of my newly shrunken world.

Every morning my husband would help me shower and get dressed (because underwear and shirts become deathtraps when you can’t move your torso). Then we’d set off slowly, down the stairs, and out onto the street.

He opened doors for me and helped me negotiate curbs and propped me up like a mannequin in cafés. He also blocked cars whose drivers were impatient with my snail’s-pace progress, and kept people from jostling me in the markets.

I felt like a burden and apologized continuously … but through it all, he reminded me that “this is the trip we’re on.”

We’re home now, and I’m slowly on the mend. (Last week’s highlight: I put on my own socks. Yay!) But I’m still disappointed about the five “lost” days — mostly because my husband lost those days, too.

Still, I’m trying to learn from his example. “Stop worrying about it,” he said yesterday. “We made the best of it.” He’s right that it could have been worse; I could have hit my head or broken a vertebra. Or I could have been alone, crawling around on all fours, injured in a foreign language.

And anyway … now we have a great excuse to go back, and to try one more time to have the perfect trip in which everything goes exactly as planned.