Fidji Simo is responsible for virtually everything Facebook’s almost 1.9 billion users see when they open the big blue app, from news to advertising. For each new feature, Simo starts by asking her teams a simple question: “What is the feeling you want people to have?” she says. “Feelings are universal.” In 2016, when Simo launched Facebook Live, the breakthrough streaming-video application, the goals were “excitement” and “anticipation.” That’s why Simo inserted a feed of viewers’ real-time comments and encouraged video creators to integrate them into their broadcasts. The interactivity was such a hit, she’s rolling out a feature called “go live with a friend,” enabling two users to broadcast together, no matter where they are. All of this has helped turn Live into a global phenomenon. Simo brings the same user-first mind-set to advertising products, which Facebook integrates closely with its consumer ones. Her approach has worked here too: Eighty percent of Facebook’s ad revenue comes from mobile ad products that Simo has helped create.