It´s not your hearing that is complex, it´s your brain!
Do you know when I experience big sound differences? If my mood changes.
Some days, I´m in a good mood and really into listening to music (or a specific piece of music) and it sounds fantastic. A few days later, I try to relive the experience, llisten to the exact same music but, somehow, it doesn´t happen. It sounds different, it doesn´t make feel the same, it doesn´t sound as good.
My set is not emotional.
How could it be? It´s a combination of machines and objects that are designed to work in a certain way and do that always (minus technical issues/defects).
Me, on the other hand, am an emotional being. I don´t function the same everyday, don´t feel the same everyday.