Every guitar player knows it: As soon as you pick up the instrument for a solo in front of a live audience, you have to make “THE FACE”… at least if you want to be considered a real guitar hero!
This is especially true if the guitar is electric, but even classical or folk players with an acoustic instrument are not entirely exempt. A simple Google search for “guitar face” will show you all sorts of vivid examples in all genres.
It’s pretty hard to pinpoint exactly where and when the fashion started, historians will probably debate this one for many years to come. I suppose it all came, like most of popular music, from the blues. And it makes sense that the suffering of the slaves in the cotton fields somehow translated to the players singing their harrowing plea.
How it came to be adopted by guitar players in particular, and in the rock scene especially, is left open to controversy. I will not adventure a theory myself.
I just know that for the many many years that I studied guitar, I have missed one essential part of my training by not doing it in front of a mirror. I would have perfected my stance and yes, probably made it big!