Doors serve as metaphors: they allow entrance and exit, and they are a symbol of protection. They also reflect local materials and culture. Much of our modern world has robbed doors of their inherent character, identity and charm, as almost any sliding glass door will attest.  Walk around your neighborhood and see how many have a personality. Great architects like Donald Judd and Luis Barragán have helped to preserve the inherent brilliance of doors in the modern world and without nostalgia, but they rarely get the attention they deserve.