I hope they - both the article authors and the trainers being described - know what the 21-foot rule is supposed to mean. A person with a drawn knife 21 feet fr

I hope they - both the article authors and the trainers being described - know what the 21-foot rule is supposed to mean. A person with a drawn knife 21 feet from you does not mean that it's time to shoot them, even if they haven't made a move towards you. It means that the time for a healthy person to run up to you is close enough to the time to draw and fire a holstered weapon that you're at risk, so you should address either the closing distance or draw time by backing off or behind obstacles or drawing the weapon before any attack starts.