Yep. I seen demonstrations where a knife wielding attacker could easily close a 20 foot distance before the victim could get their firearm out and use it.
Yup, it’s the “Tueller Drill” - pretty common rule of thumb in police training everywhere. Worse, the 20 foot distance doesn’t even account for the fact that a knife-wielding attacker can often travel a few more feet after being shot (obviously depending on where he is shot, and with what).