It was sad to see the oldest car rental institution in the world, Hertz, file for Chapter 11 bankruptcy on Friday, given the severe impact of COVID-19 on travel and the economy. But the story is a much bigger one — it reflects the difficulties of building a solid, profitable company in the car business with healthy cash reserves to survive a catastrophe; and it points to the fundamental changes in how people will be using cars, travel, and taking short rides in the city, in t