"Don't give up. Don't give in," the late WWII hero says in a new featurette

Credit: Universal Pictures

His immense courage inspired the upcoming filmUnbroken, but Louis Zamperini didn’t start out a hero.

The late WWII veteran, who died at age 97 in July, was a “rotten kid,” he says in a newly released featurette exclusively for PEOPLE.

“My excitement came from seeing what I could get away with,” he shares.

But when he began channeling his energy into running, everything changed. And many of the lessons he learned from the track would later help carry him through his darkest days in a Japanese POW camp.

“One thing you learn from sports is you don’t give up,” he says in the video. “That’s important for everybody in all walks of life, is the perseverance. Don’t give up. Don’t give in.”

Unbroken, directed by Angelina Jolie, opens Dec. 25.

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