Of all the things that could have broken Scott Jurek on a 2,189-mile run, it was a small tree root that crushed his spirit. He was 38 days into an attempt to beat the speed record for completing the full length of the Appalachian Trail, the mountainous hiking path that snakes along America’s East Coast, from northern Georgia to the top of Mount Katahdin, in Maine. Jurek, one of the greatest ultramarathoners of all times, was in trouble. After battling through a succession of leg injuries, then slogging through Vermont’s wettest June in centuries, he had to make up ground over a particularly merciless stretch of the trail, New Hampshire’s White Mountains. Delirious from just two hours of sleep following 26 straight hours of hiking, he was stumbling along the trail when he encountered the root in his path.

“As I saw it coming, I didn’t know what to do,” Jurek recalls in his new memoir, North: Finding My Way While Running the Appalachian Trail, co-written with his wife, Jenny. “Was I supposed to step around it or over it? I just couldn’t remember.” So he hit it and toppled. “I’d forgotten how to raise my legs,” he writes. “How to run like a sane person.”