Great question.
I eventually learnt not to trust magazine reviews or anyone with a vested interest.
I used to look down on pro/industry gear thinking domestic stuff was better. I tend to feel the opposite nowadays.
I learnt that there is no such thing as a definitive recording. Even if the recording remains the same, it's unlikely that the room and the system will. It's definite that you the listener won't. It just isn't possible to hear records the same way we did originally. Still we keep trying.
I have learnt that Hi-Fi is not everything. Hey, even music is not everything, believe it or not! For me tone is the best drug out there, but there's also a whole world out there too.
I even learnt to love Frank Sinatra, Nat King Cole, Bill Evans, Jazz, Instrumentals, and even Classical. 20 years ago I couldn't imagine such a thing. That kind of stuff just seemed too boring then.
I must be slowing down, in a good way.
I was always a lyrics man and music second, now it's 50/50.
One thing hasn't changed, I still love the Beatles.