I think the very first thing I learned while pistol shooting for the first time at a rental range was that "the ideal grip does not always work for everyone."
I had fired my first couple shots on a 9mm 5" 1911, and then asked the instructor (one was assigned to each first-time shooter) if my grip was ok. He said no, and then proceeded to organize my hands using guidelines like muzzle-forearm alignment (this was in a weaver stance), making sure such-and-such finger or knuckle was aligned with such-and-such part of the gun. Eventually he pronounced that my grip was perfect, and stood back to let me finish off the magazine. I have quite small hands (the "small" Hatch gloves are a little too big for me), and it felt pretty uncomfortable, but I had no idea what it was supposed to feel like to hold a handgun so I shrugged it off.
On firing the first shot (keep in mind, 9mm in a heavy gun), a spike of pain shot through my hand and wrist. I started to shift my hands a bit to make them more comfortable and the instructor jumped in to tell me that I had to get used to the "correct" grip in order to shoot properly. I tried another shot, and the pain was even worse. I set it down, and that was the end of my first handgun shooting session.
I still do not know specifically what was wrong, but my strong hand thumb joint and wrist were sore for a week. Needless to say, I never went back. Since then I've realized that, for me, exact grip placement requirements should always be taken with a grain of salt, unless I happen to have identical hands as my instructor and am shooting the same gun.