Chances are, you'll both be in motion and you won't be in a nice Weaver stance, but likely on the ground and in pain, having exhausted all other non-lethal options. Your heart will be racing, adrenaline will narrow your field of vision and make your breathing irregular. Your hands will be clammy, moist and unsteady.
And in those circumstances, you'll need to make a terrible decision that may well affect the course of your life. I'm convinced that you can't train enough - and for their part - most police officers probably do not. But having committed to the responsibility of carrying a gun, it's necessary to have a plan to use it at all times if you can't walk away, which kinda assumes the darned thing is loaded. ;-)