Steven, there's perfectly sound evolutionary reason why some people experience change in a situation where there is believed to have been none. It's all to do with response to risk.
Imagine UGG 1 and UGG2, UGG1 always feels unsettled upon returning to camp after the hunt, he always feels like things have been moved around slightly, (they haven't though). He dislikes the feeling of being unsettled and sleeps with his knife by his side.
UGG2 on the other hand doesn't notice when things have been moved very slightly and he always passes off any small changes as just his mind playing tricks. He sleeps soundly with his weapons far away on the other side of camp.
So when someone has sneaked in while they were out hunting and is lying in wait to cut their throats as they sleep. UGG1 stands a good chance of surviving, he's spooked already. UGG2 however is fast asleep, and he's gonna die.
In evolutionary terms it costs, UGG1 only a little to be in a constant state of worry, and he'll survive because of it, however it costs UGG2 his life to be blind to these small changes. Thinking differences exist when they don't in cable, stands, etc etc is exactly the same, but the risk reward is flipped.
Of course then there's UGG3, he checks the tent is safe upon his return after every hunting trip. UGG3 learns to measure his surroundings and modify his behaviour accordingly. He neither dies nor lives in a constant state of worry. UGG3 is the guy who blind tests his assumptions, he could naturally be a type 1 or type 2 UGG, but he's learnt behaviours that make his innate personality type moot.