In a time when we wouldn’t think of climbing Mount Katahdin without sturdy boots, fleece apparel, maps and freeze-dried food, it’s staggering to think that a 12-year-old boy weathered nine days on Maine’s highest peak with no shelter or food. That was Donn Fendler’s experience in 1939. And his death Sunday at the age of 90 brings to a close a life well lived, on the mountain and off.

The basics of Fendler’s account are familiar: He became separated from his family near the summit of Katahdin, walked off into the fog and got lost.

Drawing on his Boy Scout training, he followed a small stream toward what he hoped would be a settled area. The boy eventually came out at a hunting camp on the East Branch of the Penobscot. But it wasn’t an easy trek — he walked 48 miles and lost 16 pounds in the process.

Over the years, Fendler told his story — recalled in “Lost on a Mountain in Maine,” a short book authored by Joseph Egan and based on Fendler’s own recollection — to many Maine schoolchildren, and the value of determination and resilience was at the heart of it.

“I tell every one of them they have something inside them they don’t know they have,” he said in a 2011 Associated Press interview. “When it comes up to a bad situation, they’re going to find out how tough a person they are in the heart and the mind — it’s called the will to live.”

By all accounts, Fendler never tired of telling young people about his odyssey. What’s more, Fendler was genuinely interested in hearing their stories, too, and wrote back to every child who ever wrote to him, according to Ryan Cook, who’s directing a movie adaptation of “Lost on a Mountain in Maine.”

Though most of us won’t face the same challenges that Fendler confronted in the wilderness, his experiences offer a lot of wisdom to people of all ages about how to deal with tough times: Keep your head. Listen to your instincts. It’s OK to cry — it can help you clear your mind. When you least expect it, something or somebody will come along and give you the strength to go on.

Donn Fendler is no longer with us on the planet, but he’ll be with us in spirit as long as there are people who respond to difficulty with strength.