Mythbusters Never Bring a Knife to a Gun Fight

First, one must have situational awareness. It takes a moment for the brain to sort out what is happening, thus you must be aware of who and what is around you. Second, it will take time to upholster the weapon, especially if concealed. Thus, practice, practice, practice. Third, you need to know what is behind the threat, you are responsible for every round fired from your firearm.
Hopefully, you will pick the threat up at greater than 21 ft. More distance give you more options.

I've participated in training relevant to this topic... Yes; it is very realistic that a trained individual with a knife will defeat an untrained, or moderately trained individual armed with a holstered firearm at close distances. It's all about the balance of safety and efficiency available in your gear, and the amount of time you devote to training with it. Situational awareness, physical/emotional/mental strength... all of that comes into play. I'm no expert, but it seems practical to me that any self-defense mindset includes how to fight to your "tool", as opposed to relying on that "tool" as your only option.

I enjoyed their show but some of their premises are flawed at best.