Stated differently, Lukasik was arguably the first to develop that little habit that consumes the attention of so many of us—the “check-in”—the impulse triggered by the intrusive thought that whatever else one is doing: “I need to check my email.” The check-in would eventually become a widespread attentional habit; it would go on to power AOL, Facebook, Twitter, and various other future attention merchants built around various technologies and business models. No other has compelled so many minds with such regularity—regularity that has the feel of a compulsion, of a mental itch constantly in need of being scratched.

Tim Wu, The Attention Merchants, loc. 649