Together with jazz, the Broadway musical may be America's most original contribution to the arts. What's made it such an enduring form, from Oklahoma to Hamilton? It turns out, the best shows all share a few storytelling secrets, and no one knows more about that than Jack Viertel, author of The Secret Life of the American Musical: How Broadway Shows Are Built. A veteran producer, Viertel is the artistic director of New York City Center's “Encores!” series of classic musicals in concert. He's also a former drama critic and editor.