There was a moment in the early 2000s when it seemed like every child in every shopping centre had discovered the same magic trick: walking along normally, then suddenly gliding as if gravity had decided to take a break. Heelys, the shoes with wheels hidden in their heels, captured the imagination of a generation and sparked equal measures of enthusiasm and controversy. Part sneaker, part skate, they offered something genuinely novel—the ability to transition from walking to rolling with a simple shift of weight...