Think of noise as a sine wave on a Cartesian plane (the X-y graph you used in math class). The noise goes up and down so that y=1 at the max and y=-1 at the minimum.

What happens if we add 1 when y=-1? Well, now it’s 0. And what happens if we add -1 when y=1? It’s 0 again. That’s basically what noise cancelling does. It adds the “opposite” to make the sound equal 0. That’s super layman’s terms, but I hope it makes sense. It’s basically trying to make the opposite of whatever it hears.

But when something is physically touching your body, your ears can’t absorb that “opposite” sound because the original sound is kind of already absorbed in your body, if that makes sense?