...Even when it kind of is. Sorry, Chollie, but you probably didn't get the Magic Bullet-Eating Wall option, either.
Having lived alone for a goodly portion of my adult life, I am of a differing opinion than many (most?) about shooting at Persons Unknown in my house when I'm the only one there. My vision is pretty awful and in case of emergency, the order in which things get picked up is 1. sidearm, 2. glasses. Should some ill-seen large-ish shadow show up at the bedroom door twixt steps 1 and 2, things are liable to go poorly for it. ("What? You would not identify your target?" Assuming I am living alone at the time, it is identified: In My House, Not Me. Maybe other people fail to lock doors or hand out keys to friends and family, but I do not. And yes, this means I probably would have shot your hypothetical Kindly Stranger Or Policeman who has entered my house uninvited to Do Me Good -- presuming such creatures are any more real than the Tooth Fairy, which they aren't).
I don't live alone right now, which (perversely enough) means I have freely accepted a higher level of risk; once that one extra key is out there and that one other person has free access, a significant degree of control over Who Goes There has been lost and being certain that target is a target requires far more precise identification. It's the price we pay for being a social species.
And between that and the lack of those magical-backstop walls (and windows) is the reason why my house (and yours) isn't a free-fire zone. Drat! Another hallway-ninja fantasy, gone.
Working On A Starship
4 weeks ago