Disclaimer: Yes, this is an overly simplification of how a real situation would occur. But it is still a bit more advanced than the pro-guns "Gun = Protection". Not that any of this really matters at all, I live in Norway, not the States. Let them kill each other over there if they really want to…

Option 1: If both have a gun, there would have been only one choice: shoot or be shot. 50% survival rating (modified by each users skill in said gun) for both. Attacker has the element of surprise.

Option 2: If attacker only had a gun, suddenly the attacker has two options; shoot or not shoot. So he would choose to not shoot unless he feels threatened or are insane. No sane person walks around with a desire to kill. The defender also has two options: threaten or not threaten the attacker. Element of surprise is useless, as the outcome are the same.

Chances of survival increased to 75% for both persons.

Option 3: If the defender only has a gun, the attacker has 3 choices: Flee, bring fist to a gunfight, or use the element of surprise to steal the gun. The defender has 3 choices: flee (and leave the gun to the attacker), shoot or threaten. All these options are useless if the attacker is able to steal the gun. The chance for this is random, but the defender needs to have this gun close by so it shouldn't be hard to find. And one unlucky day the defender might have forgotten his gun on the table besides him, and the attacker is using his element of surprise. Chances of survival: random but small for both. Attacker might flee and return with a gun because the defender had a gun.

Option 4: No one of them have a gun. Both persons have two options: Flee or melee-fight. But both have to choose to fight for it to take place. If a fight takes place, the attacker have the upper hand (prepare melee weapons). The defender has the upper hand when fleeing (knowing the terrain). And even if both choose fight, once one of these two hit the floor, the other one have the option then and there to attempt to kill or not to kill. Surprise is usually not an issue.

Chance of survival: More than 75% (modified by each person's ability to fight or flee, and the attacker's sanity).

If i was afraid of being attacked by an insane person for a reason, I'd rather carry a concealed melee weapon than a gun. As a clerk i would not carried a weapon just because i was afraid of being robbed. The robber is there for the money, not for the kill.

And if i was ever killed by a random insane person for no other reason than he wanted to watch a man die, well... Shit happens. I could just as easily be hit by lightning or a car or something.