What do you mean?
A gun isn't some "ward evil" talisman. If the man got into such a situation where this happened to him, having a gun might not have done much more to help him out. Proper self defense is more about situation awareness and precautionary measures than it is about having a weapon or knowing how to fight. If a man is gonna sucker punch you and then stab you repeatedly, the chances of you being able to use your gun to protect yourself is somewhere on the scale between "zero" and "probably jack shit."
Except 1) if he doesn't know how to use situational awareness, his gun is useless and 2) if he did not have a gun and still knew how to exercise situational awareness, he could modify his behavior to keep himself from being a target and/or discourage the man from attacking. Guns are a last resort and if you don't know the proper steps and techniques to avoid confrontations before they escalate then I can pretty much guarantee you that your gun is useless to you.