An interesting observation is that generally, if what you are hearing sounds good and is well played, levels that are somewhat too loud can easily be overlooked, but if what you are hearing is an assault on your ears and the musicianship is poor, anything is too loud.
Some guitarists I've heard EQ their instrument so it's all twang and low end boom; this cranked up will never develop into any sort of good sound. Maybe they never heard about mids?
Victims of the equal loudness curve. The ear is most sensitive to mids at low SPL, but the curve flattens out as SPL increases (emphasizing bass and treble). Also why a good live bass tone is all mids and no a** at bedroom volume.