The main ingredient in Discover Weekly, it turns out, is other people. Spotify begins by looking at the 2 billion or so playlists created by its users—each one a reflection of some music fan’s tastes and sensibilities. Those human selections and groupings of songs form the core of Discover Weekly’s recommendations.
“Playlists are the common currency on Spotify. More users knew how to use them and create them than any other feature,”