I think what Richard is saying in the video is that when you check your gun for normal use such as every day carry, if you train yourself to all ways pull back the slide to make sure there is a round in the chamber and see brass, you will tell yourself that you are good to go. If when you are field striping your gun and you pull back the slide to check for a round in the chamber, you may mistakenly tell yourself you are good to go if you see brass in the chamber, as you have trained yourself to look for brass to make sure your gun is ready for carry. I'm not saying I agree or disagree, just trying to explain what I got from the video, and his explanation.