On Thursday evening, it seemed impossible.

Twelve hours later, it seemed inevitable.

As Friday morning’s sun cleared the hillside and warmed our campsite, I looked to the 14,252-foot summit of White Mountain, set two days of doubts aside and asked myself a simple question: “how long could it possibly take to hike a mile and a half?”

Discovering the answer was one of the most remarkable experiences in my life.

I’ve always been the doubting type, and not because my formal name is Thomas. I fancy myself a skeptic, a rationalist, a realist. Two decades of writing headlines for a living have convinced me that the only thing exceeding the human capacity for self-delusion is our tendency to allow those delusions to cause massive calamities. I’m happier not expecting much from our species.

I know about the power of positive thinking and all that, but I also know that if something appears in my mind to be just plain impossible, it probably is.

And yet, there’s the example of 4WheelBob, the wheelchair hiker who not only did something that to my mind was transparently impossible, but got me believing it was possible, too. A month later I’m still marveling at the turnaround.

On that Friday morning of our White Mountain adventure, Bob’s bull-headed determination had drained all credibility from my skeptical outlook. The reality on the ground, as they say, obliged me to stop dwelling on how it couldn’t be done and start thinking about how it could. And that’s how Bob and I were finally of the same mind: We’ve got all day to reach the top, we concluded, and besides, how long could those last few turns of gravel road take?

Of course it would be the most most grueling day of the whole outing, a 10 hour, 45 minute marathon that obliged Bob three times to crawl up the mountain on this hands and butt when the trail got so steep and rocky that his wheelchair couldn’t get traction.

I hiked to the summit a few hours before Bob got there. I kicked back, soaked up the view and even congratulated myself: it was, after all, my first Fourteener. Most of the trail to the top is visible from the summit, and every time I looked down to see if Bob was still coming, he was still coming. Inches at a time, the rocks constantly tangling those little wheels in the front of his chair, him popping little wheelies to rise over them and push up the trail a few more inches. Painfully, excruciatingly slow going.

I think I was almost as happy as Bob was when he got to the top.

Thing is, my estimates of the impossibility of Bob’s quest had been correct all along. The original plan was to hike in a mile or so on the first day, camp out and hike to the summit and return on the second day. On Thursday, the second day, I hiked most of the way to the summit and concluded there was no earthly way Bob was getting up and down that hill in a day. And he didn’t.

But he didn’t have to. If he camped out one more night and made it to the top in one marathon slog on Friday, he reasoned, somebody could hike back to the trailhead, fetch his SUV and drive it up to a point near the summit that he could hike back to. Fortunately, one of the guys in his support crew was willing and able (he even sacrificed the opportunity to see Bob reach the top), and that’s how the impossible goal became possible.

Bob could go only so far on brute strength alone. Mental flexibility (and friends who wanted him to succeed) got him the rest of the way.

And from here on in I suspect I’ll be much more skeptical of people’s estimates of the impossible.