Girl how on earth do you look like a supermodel 24/7 when you're living in a post-apocalyptic wasteland, scavenging among ruins and debris for food so you won't have to resort to cannibalism??
My old roommate just wakes up with perfect hair. Some people just got it in ‘em. I also learned how to cut my own hair in the pandemic and it went pretty well, though yea a knife a dirty mirror ain’t gunna cut it.
If you think that's bad, wait till you see all the tasteful and mildly seductive mud, blood, and gore splatters they get after surviving Space Dunkirk.
Also in videogames. The only time I've seen it could be justified happened in Detroit: Become Human. There, the character doing it is an android, so she probably got data from the internet to cut her hair properly, or was preconfigured with that knowledge.