>>12499002ground is just the origin of your chart. it's a point you arbitrarily define. it has no implication on the real world.
as an analogy, consider the word "ground" used to describe the real world. we use it to refer to "places that we stand on" but obviously this definition is entirely arbitrary. still, the concept is useful to us, as humans, because we often stand in places and would like to be able to talk about it. once you've defined what ground is, you can talk about "putting a chair on the ground" and so on. as long as we agree on what ground means, the sentence communicates the action.
similarly with electronics, "grounding" just means, "connecting a part of a circuit to the potential level we designate as ground". By common convention, we tend to use the electrical potential of the earth itself as "ground" (sometimes "earth ground", but this is just a convention.
