Again, Facebook didn’t invent tagging. It was one of those big ideas floating around the Web 2.0 zeitgeist. But combining tagging of photos with Facebook’s unique network of real social connections proved impossibly potent. We’re monkeys that like to talk to each other—that like to see and be seen. When someone tagged you in a photo, how could you help but look? Again, the primary way Zuckerberg measured the success of Facebook was by monitoring how often users returned, and how much they clicked on when they did so.
