I used to think this phenomenon was due to the state of mind I was in while listening until, that is, I had an interesting experience. One evening I had a friend over and we were listening to several different recordings and the system sounded sublime, neither one of us however mentioned anything about it at the time. Several days later the same friend came over and we listened to the system some more and the majority of what we listened to were the exact same recordings as we had listened to the previous session. Right from the start of this second session I felt that the system wasn't sounding very good,at all, and I chalked it up to my frame of mind, but about an hour into the session my friend without any provocation whatsoever suddenly says, "Why doesn't this sound anywhere near as good as the other night?" I was floored, so I asked him what he meant, he said" Well, the other night with this same recoding and all of the others we listened to your system sounded unbelievably good, and now tonight with the same recordings it sounds flat and lifeless, sterile and cold, un-involving." I proceeded to tell him that I had heard the exact same thing on both occassions and he was shocked. It opened up my eyes and my mind to the possibility that there was definitely something more than just psycho acoustics at play here.