First opener for me was hearing a properly setup system of Linn LP-12/Mark Levinson/Magnepan at Audio Concepts in Houston in the early 80s. I was in my 20s, had component systems since age 15, and still remember thinking how amazing it sounded.
Didn’t have another "wow" moment until I installed room treatment in a dedicated room just a few years ago. Biggest change, by a huge margin, ever. Truly "eye-opening". Actually "ear-opening", though I’m sure my eyes were wide open in disbelief at the transformation in sound quality.
Nothing sexy about acoustic treatment, but man does it work.
No one believes that it makes that much of a difference as they are all experts in what they know......except...this thing,this acoustics thing.. they forget......that they do not know it..
then.. proper acoustic treatment. Correct acoustic treatment. That’s the hard part to get right. To have the right lore the right knowledge and the ability to do it right. That’s a tall order, and a long way away from most folks.
So they live with their ears and brain adapting to a far more inferior sound quality. And telling themselves...it is all just fine.