Frustrated with his iPhone headphones getting tangled in his pocket, David Barnett, a philosophy professor at the University of Colorado Boulder, glued a couple of large buttons to the back of his phone to wrap cords around. It was an effective rig, but inelegant enough that his friends poked fun. Barnett refined the design through dozens of prototypes, and came up with the PopSocket. The $10 expandable button is wildly popular--pulling in $169 million in 2017 revenue, up a whopping 71,423 percent from 2014. The company expects more than 100 million of them will have sold by the end of this year, in part thanks to the extra grip on a phone it provides while taking selfies.