Comment by xwolfi

Maybe think of it more simply, one precedes the other, this much positive charge in one place attracts negative charge of equal magnitude around it: if you send more electrons (and to be honest, talking of positive charge for a proton is a bit wrong: a positive charge being the absence of electrons... and electrons giving the "negative" charge as they add up), they'll detach and push away those that were already there.

There is nothing convenient, it's as logical as saying that you were tshirts when you go out: there is nothing extraordinary that one torso = one tshirt, as having two or zero tshirts wouldn't help: 0 would make you want one more tshirt, 2 would make you want to remove one.