Well we can sit here and say: they are dumb and make mistakes, why not follow protocol, why did brett go alone etc but I think we are forgetting here: We are dealing with humans, we arent logical and rational all the time, Ripley went back for newt due to her promise and feelings to newt, not logic. Military operations never go to plan and have a lot of fubar, often soldiers will be lost alone or sent away alone, shit happens.
Afterall, if all humans followed logic and was smart, we wouldnt have had the covid virus or any plauge or disasters.
*Oh, i suspect Im sick while im in china, shall I visit a hospital and quaranty myself? Nah I will take my plan home as planned.* Covid happens. Hell not many followed the rules for covid.
People will ignore rules, quaranty etc, heck even doctors can do such mistakes. *thinking on one who got home from vacation from china to sweden with covid and ignored all warnings....*