So for the good guys that's not as sufficient as it would be for a criminal?
Actually, it's not. That's because the criminal gets to choose the time and place of the assault. He chooses circumstances most advantageous to him, and if the situation does not favor his success -- he simply does not act.
Furthermore, the criminal isn't at all concerned with killing innocent bystanders. You might even say that's part of his job description: indiscriminate killing, without thought for who else he might hit besides his intended target(s). He does not care where his bullets go.
The good person gets caught off-guard, ambushed unexpectedly. Unlike the criminal, we won't have time to mentally prepare for the encounter or ramp up our emotions to deal with the situation. We don't get the option of simply not engaging if circumstances are against us (which we know
they will be, because the criminal chooses the time and place). Because we know we will be caught off-guard, we must be well-trained enough that our reflexive
reactions will help, rather than hurt, our chance of survival. We also don't have the luxury of spraying bullets all over the place, as criminals do; our bullets must
hit the bad guy and they must not
hit any innocent people.
All of these factors make the problem we must solve considerably more difficult, more complex and more difficult to achieve than the one faced by the criminal.