History has shown time and again that when a metro area grows to depend on limited kinds of industries or companies the time comes when these generators of cash go away or become obsolete, and no one can pick up the pieces. These economic downturns leave behind social upheaval and poverty for many, until a transition to something else, which can take decades. In the meantime population emigration, poor property values and maintenance, abandoned city blocks, death of retail, a dearth of tax revenue, an increase in crime and drugs, degradation of school systems and other public amenities, etc. might go on for decades. Look at Detroit as a recent example. Boston's own frozen economy lasted from before WWI to the sixties. Good luck to those cities that are welcoming Amazon. New York is fortunate in that it's already a behemoth that ordinary people can ill afford. I just hope they know what they're in for. Short term wonder may lead to long term misery. And the day will come with Amazon morphs into something entirely different, just as the phone companies. No loss to Boston, which can continue to diversify its economy and make the metro area affordable again to ordinary people.