However, the worst training scar, bad habit, and “please don’t do this in a fight for a life” is the “unload” – “show clear” – “hammer down” – “holster”…Ugh! I have seen it countless times in shoot houses, SWAT ranges, military training, federal law enforcement and training classes. For example, they will engage a target or two and mid run will drop the magazine, lock the slide to the rear, then realize what they have done and reload the firearm and continue.

This “training scar” only occurs during poorly-designed exercises or with novice shooters. I believe the author has seen it because what he describes is known to combine poorly-designed exercises with novice shooters, though by “countless times” he really means “more than once.” It is popularly and falsely attributed to competitive shooting even though there is no evidence competitors are prone to doing it.
https://firearmusernetwork.com/myth-of-competition-training-scars/

This claimed “Unload/Show Clear scar” is an artifact of tactical theater, where trainees are told to act in a prescribed manner contradictory to what’s actually happening.

The theater script says for everyone on the line to engage a paper target in a fixed exercise on line with others doing the same, then conduct a “threat scan” (menacing scowl optional) to look for something we already know isn’t really there while pretending we might still have to engage something else, even though we really know the exercise is complete.

So, somebody failed their acting script and dropped their mag after the obvious exercise was obviously complete and didn’t perform a head wag in the school-prescribed manner… A ha! Training scar! Bad habit! Gunna gethca killt in da streetz!

I’m certain this bit of logic won’t change the minds of people that insist on imagining this imaginary problem exists. Test it for yourself.

Set up a course that doesn’t have a definite end point, where participants genuinely don’t know if, when, where, what, or how much they’re supposed to shoot. This can be arranged as force-on-force (if you have the logistics to do it right), a shoot house, surprise course, etc. The important point is to not have a predetermined end.

If there is no training scar, participants won’t run a scripted After Shooting Scan (or whatever you call it) because they’re actually looking for things that might really be there instead of acting out a scripted head wag. There won’t be a UL/SC if the situation isn’t obviously in hand. On the other hand, if someone robotically goes into UL/SC without being prompted and before the scenario is complete, you can claim a problem. But only if that happens during a properly set-up scenario.

Running surprise courses where shooters genuinely don’t know how many or where targets are in advance, where the actor isn’t required to act out a tactical theater script, will reveal if there’s a real UL/SC problem. With the exception of lower-skilled people, I doubt it will.

This is not theory. We’ve tested this very thing a number of times and find it to be the case.