Spoiler alert: If you haven't finished the video, I'm now going to ruin the surprise.
Several seconds into the film, a person in a gorilla suit walks into the frame, thumps his chest, and saunters off. The vast majority of people who are busy counting the white-shirt passes simply don't see the gorilla. Don't believe me? Try it on a friend.
Martha Beck is the author of The Four-Day Win (Rodale).
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