God Complex - S5-E23
Stupidity: Maggie and OA are searching the building. As they walk up the stairs, Maggie is using the Harries technique, but she has both her handheld flashlight and the gun's flashlight on at the same time. This defeats the purpose of the technique. Additionally, it's daytime, so the building is lit up from natural light sources, but they still have their flashlights on. (00:13:36)
Stupidity: On his own in his helicopter, TC earlier in the episode spots a very hard to catch area of vegetation where supposedly the color of the leaves is different from what's expected. However for the ending, with 4 people in the helicopter, everyone but Magnum misses a giant clearing with a bright red excavator in the open.