Introducing: The Disparity of Force
Self-defence laws do not necessarily consider intent or the amount of damage, but instead abides by the disparity of force.
When the person threatened is outmatched by one or more individuals, this disparity exists. Weapons exist as force equalizers to match the level of violence.
A smaller, weaker person versus a bigger person, an unarmed individual versus many other attacks, or even a skilled fighter versus an untrained assailant- These are all examples of a disparity of force.
Force equalizers are used to even out this disparity. By way of instance, Granny can utilize the concealed handgun underneath her wheelchair to shoot the attackers should she deem them enough of a threat.
However, even in this situation, Granny must stop shooting when the danger to her is nullified.
When the attackers flee, surrender, are incapacitated or dead, Granny must stop shooting. The disparity of force no longer exists since the danger has been nullified.
Self-defence laws are not universal, but this applies over a general scope of the world. Check with the specific location you are living in/planning to travel to in case anything happens, and you must protect yourself.