You are familiar with tunnel vision?
I've heard of 'looking through the straw' as a criticism, meaning that someone loses awareness of his surroundings.
I think the kid showed amazing restraint. If anything, he didn't shoot peoole who could have done him harm and was too slow to shoot when he finally did, letting people grapple with him before finally pulling the trigger. It really could have gone the other way.
Talk about a high stress situation. I think even well trained guys would be displaying signs of fear or anger or frustration. Rittenhouse was just autistic out there. Seems like an uncommon reaction. Organizations like the military could try to select for it but I doubt if you could teach that.
I know I wouldn't be that graceful under that level of stress. I like to think I'd remain effective but fear and anger would be on full display.