Think of it this way:
You know the part of dark matter theory that if your doppelganger from a parallel universe composed of dark matter were to touch you, you'd both explode?
It's kinda like that, but with the brain. Your inner monologue can't handle hearing your outter monologue, so it ever-so-slightly adjusts itself so that it doesn't touch with the same audio frequency and blow up. Other stuff is okay. Just not you.