Stupidity: At the beginning, young Indy knocks out the driver of the car, pulls him out, and just leaves him on the ground by the car while entering the car. Neither the knockout nor the unconscious driver lying around are noticed by any Germans in the vicinity. Not even by the soldier who opens the car door and the officer who gets into the car, both of whom immediately appear after Indy has gotten into the car. (00:06:00)
Stupidity: Kord Headquarters goes into "lockdown" after the Scarab is stolen, which in this building, apparently means allowing all the guests to leave.
Stupidity: There is no reason why any person as intelligent as Janet would keep the knowledge of Kang secret from her family. The extended Pym family are the only people in possession of the one thing Kang needs to escape. The brief explanation she gives is that she wanted to protect her family, but this makes absolutely no sense whatsoever, and she makes no attempt to explain how this secret keeps anyone safe.
Suggested correction: She is obviously scared out of her mind concerning Kang. She, through her fear, had hoped that him being trapped in the Quantum Realm would stay permanent as long as nobody knew about it in the normal universe. In that way, she tried to protect not only her family but the entire universe.
Not only does she not say that she is "scared out of her mind", she also doesn't act like it either. There is no indication that she is so frightened by Kang that she has lost her senses - quite the opposite, actually. She appears to function rationally and intelligently in every other area concerning Kang, except of course for simply telling anyone how dangerous the Quantum Realm is because the movie wouldn't have a plot otherwise. It's pretty egregious and wildly ridiculous.
Of course, she doesn't say that or act like that. But what she saw of him, when she touched his ship, scared her enough to go to all that trouble to keep him in the quantum realm at all costs. She thought it would be safe to leave, that he was trapped forever. Her judgment was wrong, probably caused by her fear. She is only human.
"Fear" is not enough to get past this level of stupidity. My point is that she doesn't act so frightened; she isn't irrational in any other way. It's just a flat-out, stupidly written element of the film that is impossible to believe. There is no way on God's green earth she should keep this secret, even after her family has made it to the quantum realm. I get that the movie is trying to say she is frightened, but this goes well beyond making any kind of sense at all; it's ridiculous.
Part of the stupidity also involves Janet's action in the mid-credit scenes of "Ant-Man and the Wasp," where she actively helped send Scott into the Quantum Realm to get quantum energy. If she was so afraid of a signal being sent to the QR, she wouldn't have let Scott go without explaining the dangers of going. This film seems to ignore that and instead seems to focus on Janet simply not wanting to discuss her involvement with Kang and her guilt, thinking no one would go back to the QR.
Stupidity: Ben passes out on the living room floor. Before Jack leaves, he places a lantern-type flashlight a couple of inches above Ben's right shoulder. Apparently, Ben's first move when he wakes up in total darkness is to move his right hand from alongside his body to behind his shoulder, where he just happens to find the flashlight. Even if Ben's first reaction is to feel for a head injury, his hand does not go high enough to bump into the flashlight. (00:02:12 - 00:02:40)
Stupidity: Kora and Gunnar arrive at the town to find the rebel Bloodaxes via a contact of Gunnar's. They literally see this contact being hauled out of a bar by bounty hunters who work for the Imperium...and then walk straight into the same bar and start openly talking about needing to find the rebels right in front of the bartender and other patrons, who for all they know are all Imperium-aligned.
Stupidity: The heroines guess the plan of the villain with a thought process that can only be explained by the fact that they read the movie script. There is no way for them to surmise that the attack on the Skrull base, perpetrated under subterfuge, was intended to "syphon away the atmosphere", and not just the usage of a really powerful weapon. Even assuming that Kamala's objection to this particular point ("they could have just invaded or used a bomb") is a logical explanation that would disqualify without a second thought the fact that a Kree warlord would use a terrifying and cost-free weapon that is also a symbol of Kree's culture just for its power, and so that it makes sense that the heroines just instantly commit to an alternative theory, there's still a leap of logic in assuming the exact next step for the Kree's quest on revitalizing their homeland (which incidentally involves randomly dumping out of the blue a gigantic quantity of salt water on a densely populated planet).
Stupidity: The "keep everyone in the stadium" plan is foiled when gold is scattered around the outside and everyone leaves. The bad guys didn't consider locking the doors? Not least because once the terrifying sky tendrils descend and boiling red clouds start filling the arena, surely people would have started bolting for the wide open exits.
Stupidity: One of the major reveals and plot twists of the movie lies in the fact that a certain character is an accomplice of the medium. The reveal, though, does not explain at all how said individual managed to fool Poirot; the trick briefly shown involves a simple rope pull to open a door. Poirot was looking exactly for that kind of trick, paces around the room constantly on maximum alert, and examines the door itself later. Likewise, it does not explain where and how they could hide the stuffed animal.
Stupidity: The mercs are said to drop in, in broad daylight. Approx four men are furthermore able to drop with plenty of ammo and at least one high calibre rifle, but they do not bring mines to secure roads nor drones to map the area.
Stupidity: The patient was wearing a white and gray striped tie when he was walked into the ambulance. The EMT did not remove or even loosen the patient's tie (to facilitate breathing). Instead, the tie was moved from the front to along his shoulder/neck, apparently to get it out of the way while she was cutting off the patient's shirt. (00:07:50 - 00:08:20)
