Stupidity: So if Harley Quinn drove the truck to blow up the plant, wouldn't she have had to drive through all the cop cars at the bar murder scene? We know it was the same street because the cop gives the necklace to the detective. (00:10:58)
Stupidity: Molly was being hunted and didn't know if she could trust Rayburn when he encountered her. Rayburn told Molly that he wanted to help, wouldn't hurt her, put a blanket around her, and even carried her in the woods for some distance. When he put her on the ground (along with his backpack and rifle) to go find the rope to open the pitfall doors and had his back turned, Molly got out from under the blanket and hid nearby. Rayburn quickly found Molly, and Molly made a lame attempt at attacking him with some kind of club. The next day when Rayburn and Molly were in Rayburn's house and her hunter showed up and attacked Rayburn, Molly grabbed Rayburn's rifle and fired several shots at the hunter. Molly obviously knew how to use a rifle, so it was asinine for her to have hidden from Rayburn the previously night without taking his rifle (or the blanket). (00:36:22)
Stupidity: Becky possessed the mysterious key that the four neo-Nazi prison escapees were at the lake house to retrieve. Becky didn't know what the key was for, so did not have a vested interest in it. By first denying that she knew where the key was and later refusing to give it to Dominick, her father was killed. Had Becky simply handed over the key when Dominick asked for it, it is possible no-one would have been hurt/ killed. Becky keeping the key with no importance to her served to further the plot.