There are two areas of the human body where a single shot even from a 22lr can bring the perp down immediately: the brain pan and the bladder and surrounding nerve-heavy area. One is a lot more painful than the other, but I’d rather a perp be writhing in agony screaming on the ground than still coming for me after the first shot to the center body mass..
I was in a training session where I was told that the groin/pelvis area was an excellent target for stopping a knife-wielding assailant. It puts him down on the floor instantly (something a center-mass shot is not guaranteed to do, especially if the bad guy is drugged up) and is easier to hit than the head.