Construction continues on Mass + Main, a project that will add three buildings and 306 apartments to Cambridge’s Central Square. The taller of those buildings will run to 19 stories and 195 feet, placing it among the highest in Cambridge.  The project is scheduled for completion in the fall of 2019.  Soon the building will block the morning sun that falls on the Clover restaurant where I have breakfast most days.  It is a stark reminder that the things we take for granted are rarely permanent.