A person with a knife can cover at least 21 feet of distance before a skilled gun handler can clear leather and get an (one) aimed shot off. Service pistols are not nuclear weapons, and quite often do not result in one-shot stops, particularly with those on drugs or mentally ill. So when your first shot either misses, or fails to stop the assailant as he rushes you and cuts your throat, you’ll have a few seconds before expiring to congratulate yourself on your restraint.
Exactly. A knife at 21 feet is as dangerous as a suspect with a gun. It is well known that gang members in prison practice and plan to charge from 21 feet, bent at the waste and reach down and touch one hand on the ground momentarily as they charge because the officer trains to shoot center mass. By doing this the criminal will be below the center of mass height, if their hand actually touches the ground when they charge and the officer’s first shot will miss them.