So I bought a new bike this week, but have sold two others since. I orignally had 4, then 4+1, then 5-2, for a total of three, or N-1. My wife contents that I still owe the family budget money to cover the new bike. I on the other hand content that she owes me another bike because you CANNOT be at N-1. So to restore balance to the world, it needs to be (N-1)+1=N.
It's kinda like Einsteins Theory of Relatives.