Prometheus was the god of forethought in Greek Mythology, but that's not an attribute displayed by the Prometheus cast.
- The ship has just landed close to an obviously artificial structure, but there are only a few hours of local daylight left. Holloway wants to explore the structure immediately.
You'd expect: Vickers or Janek would shut him down and point out that they shouldn't go anywhere without plenty of daylight and ideally a better understanding of local conditions.
Instead: No one raises more than a token objection to the expedition setting out immediately. And apparently little attention is paid to local weather patterns.
The result: An extremely dangerous storm kicks up with only 15 minutes of warning; most of the expedition makes it back to the ship just barely in time, but two members can't get out of the structure in time and are stranded overnight, resulting in their deaths. - The ship has landed on the planet and they are exploring the Engineer structure in their spacesuits. Holloway detects with his scanner that carbon dioxide levels are low enough for the air inside to be breathable.
You'd expect: The crew to wait to perform analysis in order to rule out the possibility of microorganisms, pathogens, or any kind of hazard the air could be carrying before even considering working without their suits. Still, even although it were deemed to be safe, they should keep their suits hermetic anyways in order not to RELEASE any terrestrial biological residue that could infect and/or modify the environment. Most of the crewmembers are either scientists who will know the importance of asepsis in an exobiological research or space pilots who should be familiarized with the consequence of not following containment protocols.
Instead: Deciding that not choking in the atmosphere is fair enough for him, Holloway takes off his helmet.
Even worse: While other crewmembers do object to it, nobody tries to stop him. Instead, they imitate him once they see the air is really breathable.
The result: Nothing this time, but in an alien planet with unknown lifeforms it could have caused literally anything. The next film, Alien: Covenant, would show it in a very graphic way. - Two members of the expedition team (Fifield, a geologist, and Milburn, a biologist) set out to leave the alien facility and return to the Prometheus. The first of them is the mapmaking expert of the crew and the controller of two floating cartographic drones that are presumably still mapping through the tunnels.
You'd expect: Them to reach their destination safely. If they get lost, all they have to do is check Fifield’s wrist computer for the three-dimensional map of the corridors he just created.
Instead: They get lost, but neither of the two thinks of doing such a thing.
The result: The next point. - Fifield and Milburn come upon a pile of corpses who all have exit wounds in their heads. They radio in to the ship's captain, justifiably freaked out, and tell them their position. Janek tells them he's been getting a glitch from one of Fifield's mapping probes that is situated at the end of a long corridor.
You'd expect: That, since Janek can see the stranded team members' location on his comm system and can direct them, he would tell them to wait near the entrance of the structure until morning. Or, failing that, he would tell them to stay exactly where they are and not touch anything—literally, anything besides the course of action he takes.
Instead: Janek laughs at their discovery, acts like the glitched probe isn't a problem, and leaves them to wander around some more in the structure. A few minutes later, he goes off to have sex with Vickers and leaves the comm station unmanned.
The result: Milburn and Fifield are left to their own devices, leading to the next point. - Milburn and Fifield are camping in the "big head" room, where they discover that all of the jars on the floor are leaking black liquid. A snake-like creature emerges from a pool of the liquid and Milburn wants to examine it. Fifield tells him this is not a good idea and that they should leave immediately.
You'd expect: Them to leave immediately and not look back. After all, both of these men were smart when they bugged out during Shaw's discovery of the first Engineer body in this very room. Milburn is also a biologist, so he should completely know the risks of approaching an unknown creature. Even if he is really that fascinated with the damn thing, it's much safer to retreat for now and maybe return later with a support team and adequate tools to capture and analyze the creature. Heck, even someone without an extensive education in biology would probably notice the creature's striking similarity to the terrestrial cobra and give it a wide breadth.
Instead: Milburn continues goading the creature, and even begins stroking it.
The result: The creature latches onto Milburn's arm and breaks it, which leads to Fifield falling into a pool of the liquid and having his helmet melt into his face. - Captain Janek receives Fifield's signal in front of their cargo door. He tells the crew to open it to check him, and they all see what seems to be Fifield's corpse bent over in a bizarre posture.
You'd expect: The crewmen to approach it cautiously and with weapons in hand. They have just witnessed Holloway getting horribly mutated and have every reason to think Fifield might have suffered the same fate.
Instead: They stroll towards it casually and unarmed, and one of the crewmen even goes to kick it.
Even worse: Janek clearly senses something is wrong with the body, yet only mumbles to himself instead of yelling at his crewmen to stop and take caution.
The result: The thing gets up, revealing itself to be certainly a mutated Fifield, and promptly wreaks havoc, killing at least three men. - Holloway wakes up a day after running around on an alien planet with no helmet (not the cause, but the most reasonable assumption based on what he knows), looks in the mirror, and sees a worm swimming around in his eye.
You'd expect: Him to notify the others and have himself placed in quarantine or at least medically examined.
Instead: He says nothing and heads back out on another expedition.
The result: He starts rapidly deteriorating while they're in the alien ship. The others notice and try to rush him back to their ship, but by the time they get him back his face is turning black and bubbling up and he's begging to be put down with a flamethrower. - Shaw realizes that she had sex with her boyfriend after he'd been infected with a biological agent that heavily mutated and killed him. She's pregnant—despite being sterile—and a surgical suite extracts a freakin' octopus monster from her womb.
You'd expect: Shaw to alert the ship's medical team that she should be placed in quarantine to see if she's infected, or- at the very least- tell somebody that there's a mutated octopus monster in the captain's cabin.
Instead: She doesn't breathe a single word to anybody about anything that happened, and the octopus baby is completely forgotten about until it becomes Chekov's Gunman and kills the rampaging Engineer at the very end of the film.
The result: Actually nothing, but it's only by sheer luck no other crew were killed by the thing. - Mr. Weyland orders David to wake up the sleeping Engineer in order to convey his wish for more life.
You'd expect: That he understands they are dealing with a creature whose motivations, abilities and power (or even sanity, as it's likely the last thing the Engineer saw before going to hypersleep was the dramatic demise of his race) are completely unknown, and as such, that they have to act with extreme caution in their interactions with him.
Instead: As soon as the Engineer is awake and looking at them, Weyland orders David to issue not a request, but a demand, without any kind of introduction or preparation whatsoever. (In a deleted scene, the Engineer gets understandably angry at this, yet Weyland still addresses him in a way that, even by human standards, would be incredibly rude and overbearing.)
Even worse: Weyland orders one of his bodyguards to hit Shaw while in front of the Engineer, thus offering him a free show of how petty and violent humans have become.
The result: If the Engineer wasn't already convinced he had to destroy mankind and reinitiate life on Earth, he probably became so by this point, and if he was, it didn't help a bit. He kills Weyland and his crew and activates his spaceship to carry on his plan. - Shaw and Vickers are seeing how the fallen Engineer spaceship has landed on its round edge and is tumbling towards them. They run away before it crushes them.
You'd expect: That they look around in order to try to pinpoint where is the spaceship going to finally stop in order to avoid the place. Their helmets allow enough peripheral vision to get a good view over their shoulders and it will not take much extra time.
Instead: They run in a straight line from their initial positions without ever considering the possibility they might be running to their deaths.
The result: The spaceship catches up with them, crushes Vickers, and almost crushes Shaw, who trips over and only then comes up with the above solution.
