> To take more extreme example, first thing you expect from housing is a protection from elements. So according to YAGNI, you should build the roof first, and see if it's good enough for you (and you don't bother, for instance, that you can only stand in the middle of the room). Again, no one really does that with real houses.

Maybe they should. I once stayed in a house with no internal walls. It seemed weird at first, but then I realized I actually quite liked it.