I had to pass a series of psych tests before I was sworn & authorized for firearms. Regretfully my authorization was on my warrant which I gave up when I had to resign for medical reasons after 9+ years.
I just want to relate an incident that happened to me about a year in. Myself & my partner were supervising a beach front bar at closing. We stayed outside until most had left. There was a big guy who was not leaving, holding a bottle (potential weapon). I knew I was going to have to confront him & indicated for my partner to watch my back, in case he had friends.
I approached him & at about 2 paces, I told him he had to leave. He had the bottle in a weapon hold by the neck. He was a little bigger & probably stronger & I had to keep my right forearm over my M19 loaded with full house 357s. We locked eyes for a few seconds... it seemed longer. In those few seconds... I cleared my mind that if we went to the floor, I would shoot & in all probability kill him. A flash of recognition crossed his face. He tossed the bottle in the trash & left. He hadn't actually done anything chargeable... yet.
The imprint of the target stocks was deeply impressed in my arm & the occasion in my mind.
I had not recognized the subject since he had completely changed his appearance since our first meeting... the subject was a wife beater & sometime druggie, kicked out of the Army during the height of Vietnam for the good of the service, had done hard time for attempted murder... subsequentally went on the run for several years for another serious assault charge... long enough for the critical witness to die in an auto wreck. I saw him several more times in official capacity but I never had another problem with this man...
It is all well & good that you should, in fact must, think about this ahead of time. But it is different when you face the dragon for the first time. Despite my preparation, there was a few seconds when I was not mentally prepared. Once I resolved it in my mind, the opportunty was lost... and he knew it.