For most of the 20th century, popular media was a monolith. Three major television networks, a handful of movie studios (the "Big Five"), and major record labels dictated what the public consumed. Entertainment was a top-down, one-to-many broadcast. If you wanted to be part of the cultural conversation, you watched the Friends finale on Thursday night. You bought Thriller because every radio station played it. You read TIME or People to know what was important.