It's also why police don't let people who are "unarmed" close to them. There are police training videos which show just how fast someone can close a distance of even 30 or 40 feet and attempt to take your gun. They are very eye-opening. It's best to keep some kind of cover between you and the bad guy.
I heard 21ft in 1.5 to 2 seconds. You have to practice regularly to hit you target in under 2 seconds from concealment. So practice.