The first decision in a design process may be arbitrary. After that every decision can be measured and evaluated against the first and subsequent decisions. This idea derives from the tradition of imaginary, theoretical or paper projects where sites were often made up or non-existent. Knowing where to start was difficult, so the architect and educator John Hejduk allowed the first move to be arbitrary or unmotivated. However, once you commit a single line to paper, the site is transformed, weighted, accentuated and articulated. Every subsequent design choice can be evaluated and critiqued as either enhancing or detrimental. Although this idea came out of a kind of architectural ‘game’ its important point is that very little if anything at all should be arbitrary in design. The way a building sits on a site transforms the space around it. The way a wall is positioned and articulated transforms the space on either side of the wall. Rooms are not just spaces for what happens inside but forms that impact on what is outside the room. It is, in short, a reminder about the fact that architectural design is about creating relationships among things; structuring spaces in relation to each other; and that nothing should be exist ‘for its own sake’. However much you might want something to exist ‘for itself’ if it is in the world, even as nothing more than a line on a piece of paper, it is in relation to its surroundings and is subject to evaluation and critique.
Source: I picked up the line about the arbitrariness of the first move from John Hejduk so long ago that I cannot recall where it was I read or heard it.