Sorry...Just to be clear I'm sure plenty of people do it and are good that way.
It's just the guys I've worked with aren't.
There's one guy in particular - I'm convinced he *needs* to hear himself because he thinks he needs to hear himself.
I've told him over and over to slip a can off and judge his performance the same way he would live, in the shower, in rehearsal.
It's strikes me as fucked up to practice, rehearse, hone a talent or skill under one set of circumstances, then come into to create an important and permanent record of that skill with the goalposts moved.
I find the fader for the performers volume is an inverse volume control and I seriously use that as a tool. When I want the guy to sing louder I pull his fader down, and vice versa.
As long as he doesn't notice, it works great but like...seriously...Pop a can off and learn some mic technique.