There's only one (non-fatal) way out of my apartment. If you're armed and running in any OTHER direction, you're going to stop a bullet. Even then, I don't know for sure that you're not running for cover, which is right next to the door. I'm not letting you get between me and my only way out. If shooting you in the head with my Model 29 is the most efficacious way of preventing that, then, as the youngsters say, "I'm down with that". You weren't invited in the first place.
An armed man, in my home, blocking my only way out... that's the very definition of "reasonable fear of life and limb".