CONCORD, N.H. (AP) — While setting a speed record for New Hampshire hiking, Philip Carcia was sometimes struck with a sort of reverse déjà vu. Halfway through a hike, he'd question whether he had completed an earlier one on his list.

"I'd get fanatical about checking that I had been to peaks," he recalled. "I'd think, 'I can't really remember, was I on Cannon in February? I don't have a vivid memory of Cannon in February.' And I'd start to kind of panic a little bit. As soon as I'd get home, I'd look at my data and see the notes and think, 'Phew, OK, cool, I was there. OK, we're good.'"

Given...