When Fleet Foxes singer Robin Pecknold was in high school in Seattle, he was overweight, bad at sports and way too into The Lord of the Rings. "It was a pretty isolating time," he says. "I was never invited to anyone's party. I felt invisible." If that wasn't bad enough, he suffered allergies so debilitating he was often unable to go to school. "Once, I sneezed 23 times in a row," he says. "I could barely leave my house. My face would turn red and I'd, like, die."

But he did have a...