I've heard the story before, as it related to my Criminal Law course, about the fact that eye witnesses, while so heavily relied upon, often have conflicting versions of the same account. While each truthfully believes what he saw, their stories are often dramatically different.
As it relates to concealed carry and the "exercise" in the classroom of having two men come in and argue with a knife, I think there is another lesson to be learned. Things aren't always as they may appear and as CCW holders, we need to evaluate the situation if and before we decide that intervention is necessary.
Another thought that I was just reminded of, relating to observation: Shortly after 9/11 I needed to pick up a girlfriend at the airport. This was in the heighted security checkpoint a mile from the airport days, where an inspection of every car was necessary. I had recently been at the gun range and my .357 and boxes of shells were in the trunk, concealed only by a biodegradable plastic grocery sack. I forgot about it until I was literally being searched. The officer was not very observant because he looked in my trunk and told me to carry on. I was glad that I wasn't harassed about it, but at the same time NOT reassured about the level of alertness of the guards.
After that, and also knowing a TSA worker, much of the 'security' at airports are feel good measures and nothing more.