This is very simple but I never actually noticed it before. Say you put down a wall on a foundation piece, and next to that foundation piece is another foundation. Now you have one wall sitting “between” two foundations. Make a third foundation and place it on top of one of the two and you have a wall that is up against your last foundation piece.
Buuuuut…you can’t put a wall against a foundation piece, it will never work. You put up the wall first then the foundation. Why does this work one way? Why not both?
I’m a big fan of making basements, I wish I had known that before. Now I can give future basement sexy walls instead of always just foundation “walls”.