> Empirically, what seems to kill cities is crime, or the death of some industry they depend on. That second cause is interesting. What if, instead of dying,

> Empirically, what seems to kill cities is crime, or the death of some industry they depend on. That second cause is interesting. What if, instead of dying, the industry were to just leave? San Francisco's benefits are built on network effects, and if the network shifts away, why remain?