“Introverts of the world, unite!” A few galley copies of Susan Cain’s eagerly awaited book, Quiet: The Power of Introverts in a World That Can’t Stop Talking, arrived at The Lavin Agency’s New York and Toronto offices today. In the book, Cain shows how dramatically our culture undervalues introverts (who make up roughly a third of the people you know) and identifies the advantages of being one. “Mark my words,” Guy Kawasaki says, “this book will be a bestseller.”