Of course we're speculating, there is no universal "wiring diagram" for humans and there never will be, I'm afraid. I'm not a neurologist, so what I'm saying is based on my practice and own experience. To your question, what "one doesn't listen only to..." means, quite simply: We are listening most of the day to a variety of sound sources, many if not most of them "chaotic" natural sources, and (unwittingly) compensate for "errors". If one would just listen to another stereo system, the chance to "locate" the error would be higher, because it would be seriously bad luck to come across two systems with the same issue. Back to the example of the "cerumen obturans" patient: Subjectively no problems, objectively one ear blocked by earwax completely, probably for weeks. After rinsing, the previously blocked side will sound louder/brighter, but just for a few hours. Seemingly, the brain decides "that way is the right way", just as it previously had adjusted for the blockage (which again took days to weeks to build up). Stereo hearing with two speakers is a bit of a mess anyway, in most setups/rooms, but the above refers to hearing physical sources. Another factor is "sound awareness", people who have impaired vision tend to hear more (or more accurately) than those with perfect vision, another compensation mechanism. Again, my own example: I could never work in an environment with "muzak" or even radio running all day, others don't even notice it during their work day, they get to ignore it like a bad smell. It's all as fascinating as it is still largely "uncharted territory".