“Millions of Swifties and KatyCats—as well as Beliebers, Barbz, and Selenators, and the Rihanna Navy—would be stunned by the revelation that a handful of people, a crazily high percentage of them middle-aged Scandinavian men, write most of America’s pop hits. It is an open yet closely guarded secret, protected jealously by the labels and the performers themselves, whose identities are as carefully constructed as their songs and dances.”