The one time I drew my gun for real I should have learned that lesson, but still haven't.
(To make a long story short- I walked in on a break-in, and found a guy standing by the busted open door with a crowbar in hand. When he approached with the crowbar I talked him into leaving. When he did, I relaxed. That's when the guy who was inside the apartment ran out the apartment door, past me, and out the front door. He was gone before I knew he was there. The fact that scanning still wouldn't have let me see him doesn't matter because I didn't even try to see if anyone else was there.)
I still have a hard time doing a 360 because of looking vs seeing. I usually scan about 45 degrees in either direction. Any farther, and I'm looking vs seeing, and my feeling is that I might as well be looking at the known threat.
I should look anyway and spend more milliseconds on trying to see, but then I worry about spending too much time away from the known threat.
The proper solution, of course, is to see wherever I look, and to look everywhere.
I've wondered if perhaps the ideal way is to circle the down threat and look over/through/past them for threats in a 360, but that may not be practical.
Anyway...
I think it's like most things: What you should do depends on the situation.
If you see tempers flare and one guy goes off on the other and starts shooting, it's probably at least 50-50 he is the lone threat and OK to devote most of your scan to him.
But if you shot some nut who just pulled a gun out and started blasting without provocation, you don't know if there are 50 more around with the same plan and you might be better off forgetting about the first guy ASAP and start looking all around.
It's like everything else:
You never know. So you just try to practice everything you can.
