I hear my back door kicked in at 3 in the morning, I put on my glasses and load my pistol. My bedroom door opens, there's a man with a knife. I fire one round. That round pierces his heart and he dies on the spot. Justifiable force.
Instead, I fired two or three rounds in quick succession, because one round might miss or fail to stop him. Very likely justifiable force. Like any person wouldn't pull the trigger a couple times in that scenario, right?
Instead, I fire one round. It hits him in the chest and does serious damage to one lung. He drops the knife, staggers into my living room and collapses. If I shoot him again to finish him in that state, that's murder.
I recommend against breaking into houses on this continent.