Nicolas Kemper:

Accretive projects are everywhere: Museums, universities, military bases – even neighborhoods and cities. Key to all accretive projects is that they house an institution, and key to all successful institutions is mission. […]

So, why do cathedrals take so long to build? Because the finish line is besides the point. Cathedrals are so compelling because they make visible the continued commitment that every building, city, and institution requires of their participants if they are to survive. Cathedral building ritualizes construction; they are compelling because they are never finished.