Aim only for the center of mass
If the threat is continuing and you only have one bullet left what do you do? Do you save it for yourself? Do you perform a head shot and hope it works? Do you shoot center mass and hope this one instantly stops the threat?
You have a five shot revolver and 3 gentleman aproach you. One of them pulls a knife and threatens your life. Do you only shot COM and hope you stop the first one in two shots? Do you modify your failure drills to give yourself a fighting chance?
I'm not saying that these are common scenarios. I am saying that blanket statements often ignore the nuances of self defense.