Everyone knows "David and Goliath" — the shorthand for the scrappy underdog, the little guy who somehow wins despite impossible odds. It's one of the most reached-for phrases in the English language, deployed for everything from sports upsets to courtroom battles. But most people invoking it have never actually read the story.

Megan Phelps-Roper knows this story intimately; it was practically her family's origin myth, the one they told about themselves, again and again, standing alone against a world of giants. But going back to it now, she's less interested in Goliath than in the fear that gripped everyone else — and in the uncomfortable question of what separates real courage from poisonous certainty.

This is a story about how the same courage that lets you stand up to a giant or a mob can, if you're not careful, curdle into the very thing it once stood against.

After listening, please share your own stories as well as your questions and comments below.