In 2006, John Zimmer was a college student and ride-hailing wasn't yet "a thing." But a class on green cities got him thinking about the glut of underused cars on the road. Eventually, he co-founded Lyft, a company that has helped make ride-hailing a fixture of American urban living. PLUS in our postscript "How You Built That," an update with Kyle Ewing, who almost set fire to his living room making Terraslate, a tough waterproof paper.