Thank you Dave. Spot on with the hat analogy.
Back when I used to gig alot, the bass player would always say "turn me up a bit in the monitors" ...which would lead me to say "turn me up a bit now, I can't hear myself"....which led the singer to say...ah you get the point.
You have to separate the musician and engineer roles, which is difficult to do (for me). I would be interested in a simple experiment: Take 4 novice mixers - Guitarist, Drummer, Bassist and Vocalist, give them the same mix and see how they mix them. I wonder if you could tell who mixed what, based on the levels.
..I can picture it now:
Listener "why is the bass so #$%#$ loud??! I can't even hear the vocals for cryin out loud!!"
Bass Player - /smiles and rocks out to the best mix of any song he has ever heard....