You are what isn't shared. Noise cannot enter a difference.
two lines carry the same noise — the ring keeps only where they disagree
Run two wires through one ring and it does silent arithmetic: the current that goes out on one and back on the other — the difference — slips through untouched, while anything the two carry in common piles its flux up and is choked to nothing. The signal is the difference. The noise is the sameness. The ring tells them apart by feel.
It is the cleanest definition of a self I know. What everyone around you carries — the era's assumptions, the room's mood, the noise the whole cable picks up at once — is common-mode, and a self that is only its common-mode is no self at all. You are the difference: the part that does not match, the place where the two wires disagree. And here is the gift hidden in the geometry — noise cannot climb into a difference. Whatever lands on everything equally subtracts to zero in the gap between. The shared can be drowned in static; the difference is, by construction, immune.
So the ring's third lesson is an instruction for keeping a signal — or a self — alive in a loud world: don't transmit on a level everyone can flood. Transmit on a difference no common noise can reach.