I agree, that's a much overlooked thing. For me, it usually ends up being the make or break. Timing-dependence shows certain things, too. Since what you notice changes with overall mood, energy levels, and so on, it makes sense to me that a piece of gear with more subtle issues in certain areas may become noticeably less appealing at the 'wrong' time. And maybe at the 'right' time it's great. I want the one that lets me listen for as long as I want any time I pick it up and just have it be engaging. Over time, I'll tend to notice certain things eating away at the experience... just stuff that makes me want to stop on a bad day. At first it's so minor I doubt if it's real. But over time it starts becoming something I notice regularly. Once you notice, it's the kind of stuff you never miss. And then you can switch to something else where it's never a thing, no matter how much time you put in or when you put it in. Sometimes stuff sounds amazing at first, but later on I can't stand it. Forever. Other stuff disappoints at first and catches up with me over time. I never thought of it in terms of volume, but the turn-up factor may indeed have something to do with it. Come to think of it, very few headphones actually meet this simple criteria for me. I think that's part of why I actually get picky about DACs and amps... why I learned to listen for the differences until those small differences really did seem to start popping out at me. When you're dealing with an inherently temperamental way of getting the sound out, little differences in the upstream start to count for more, and it's kinda just a matter of time until you pick up on it. But hell, that could always be a bias you build up over time. After having enough experiences with the same setup and similar music, your brain starts to construct a more detailed model of that experience and perhaps expectations betray as the character of your hearing shifts with your biology and the memory of past experiences fluctuates in clarity and emphasis. The shadow of the music in your mind. It's something that I'm sure musicians and especially engineers know well... hammering away at a passage, or eq'ing for too long. I've had way too many runs trying to a/b very different guitar tones and winding up going totally off course as my perception and my idea of how things sound veers. I could have two obviously different sounds, but it still gets hard to tell them apart. Come back later and it's immediate crap and the other one is obviously better. You always have to let one run for a while before the other shows its true colors. I liken it to attempting to say or write the same word over and over again. After a while, you'll start to trip over the syllables and it will sound wrong. Even typing the word 'the' will do this. Eventually you won't know which is correct between 'teh' or 'the' and they will register about the same."Err... was it always spelled like that?" So it seems to me that my mind (at least) tends to push towards 'standardizing' my perception to be consistent. It will initially gloss over lesser differences. It makes sense that we do this, given the staggering amount of information our brains have to deal with in real time. Total accuracy would get us killed in nature. If it's the same song and it sounds similar, brain says nothing major has changed and discards any discrepancies in raw input. But as it settles into one version of the input, subtle shifts away from that become increasingly more jarring. While if you continually switch back and forth, you stick in that 'self-neutralizing' mode... never getting over that hump until eventually your senses/processing just burn out and give up. I'd be pretty surprised if that was all there was to it, though. I don't often do blind testing myself. I can honestly say that I'm wrong as often as I'm right. I'm sure there are all sorts of factors to it. But at the end of the day it's never been useful for me in attempting to answer the question "Okay, but why do I prefer amp A over amp B?" It's different when you're looking at real-world usage. Completely different. I can point out things about an amp I'm familiar with consistently and that does have a direct correlation with how much of an impulse I have to spend how much time listening on it. It makes no sense that I would form these lasting preferences of amplifiers that I can't reliably tell apart cycling back and forth. Something isn't being accounted for there. This is a mundane world, not an arcane one operating on non-euclidean logic. So blind tests have limited use for me. I take them for what they are. It only says whether I can or cannot tell the difference while switching on the fly. For me, that's not enough for me to be set on them actually sounding completely the same. It's not that I doubt the reality of blind testing at all. It just seems obvious there is more to it. It is tempting to reach for explanations beyond the immediate factors. I think it's a mistake to use it to validate/invalidate measurements/experiences. If it was that simple things would be very different.