stone and stucco buildings had thick walls, 18" - 24", and the space of the door, its narrowness and height, created a compressive space that allowed for a momentary pause before entering a building. The distinction between inside and outside was not so quickly blurred with sliding glass doors and picture windows. Inside was safe and warm, and the threshold, the eyes adjusting to the diminished light, was the moment of arrival.
In Colorado we often revel in making large, transparent openings that extend the inside space of our houses and offices into the landscape. Massive sheets of glass capture panoramic views, sun-streaking floors and projecting us out to the mountain beyond. However, when everything appears as open, have we negated the thrill of that radical exposure? I think Frank Lloyd Wright's simple houses had a more nuanced approach - wide open doors and windows to extensive terraces and gardens, but buttressed with a deep, heavy masonry fireplace at the heart of the house. This at least rendered the entire space as a kind of threshold, a spectrum from inside to outside, rich in its seasonal variability.
Too often an architecture of "lightness" sacrifices the deep, velvety darkness that can also be a part of a house. Architects may associate "cozy" with over-stuffed furniture and fussy wallpaper, but they have often unnecessarily given up this feeling of warmth and hearth in over-aestheticized notion of "modern" living.
(The FLW photo is of a typical Usonian design, the Winkler/Goetsch house, in Michigan, 1939, from H.R. Hitchcock's In The Nature of Materials.)