Apollo 11, the JPEG, and yes, even the Roomba. : Back in 2009, Facebook launched a world-changing piece of code—the “like” button. “Like” was the brainchild of several programmers and designers, including Leah Pearlman and Justin Rosenstein. They’d hypothesized that Facebook users were often too busy to leave comments on their friends’ posts—but if there were a simple button to push, boom: It would unlock a ton of uplifting affirmations. “Friends could validate each other with that much more frequency and ease,” as Pearlman later said.