Let's say I wish to walk from the spot I am standing 5 feet forward. I do. I am now five feet from where I began. If I walk 7 feet in the opposite direction, I can represent this on the number line like so:
-4__-3__-2__-1__0__1__2__3__4__5__6
I started at 0 and walked five feet forward. Now I take away 7 by walking backwards.
-4__-3__-2__-1__ 0__1__2__3__4__5__6
I don't end up one foot behind where I started. I end up 2 feet behind where I started. I note this by placing a " - " sign to indicate that I have ended up behind where I started. Mathematics is all about precision. I can add apples and oranges if I say that 4 oranges plus 5 apples is equal to 9 pieces of fruit because I am actually not adding oranges or apples but pieces of fruit. What I can't do is say I have 9 apples.
You started at 1. You took 5 feet forward. Your at 6. Take 7 steps back, your at -2.
Still 2 steps away from where you started. Just the zero doesnt belong. You atarted at somewhere. Not nowhere.