I find it interesting that the pawn guy allows the guy to advance on him while at gun point, then physically tries to stop the BG when the BG grabs the gun. Then shoots the guy as he's running away. I'm not trying to second guess his actions, but trying to figure out what the tipping point was for the pawn guy.
As you have alluded, there's no way for us to know why someone would hesitate vs. act.
But I'm afraid that some might hesitate due to the publicity the surrounds some shooting cases -- such as the Trayvon Martin incident -- and the resulting fear that they might become become the the subject of a media circus.
I'm surely not suggesting that anyone should hesitate to defend himself when facing potential death or great bodily harm. Just saying someone might.