What Isn't shapes what Is.
Interior and exterior spaces are shaped by walls, but the movement of energy through and among these structures is what makes spaces livable, heatable, or defensible. This quote from the East-West architectural book, The New Asian Home, by Kendra Langeteig:
"We pierce doors and windows in making a house; it is in these spaces, where there is nothing, that the usefulness of the house depends."
- Lao Tzu