A really good example is the autism issue. Whenever a parent has a child who ends up being autistic, the parent more than likely says, "What caused it? How did it happen? Is there anything I could have done differently?" This is part of the reason why people have been so down on the M.M.R. vaccine, because that seems like a proximate cause. It's something that usually happened shortly before the autism symptoms appeared. So our minds immediately leap to the fact that the vaccine causes autism, when in fact the evidence is strong that there is no link between the M.M.R. vaccine or any other vaccines and autism.
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This is the problem with CFS. On the surface, it seems entirely random -- often affecting people who have good health/exercise habits -- so the doctors blame the one thing they can: psychology. The patient who exercises daily and eats her veggies, doesn't drink or smoke, obviously can't be blamed for bringing it on herself (unless the doctor wants to accuse her of lying about her health habits), so he goes for the one thing that's hard to prove or disprove: what's inside her head.
The first doctor I saw in 1987 kept harping on psychological causes, finally going through a long list of things that might produce anxiety. With that prompting, I finally remembered that I did have a minor legal matter in process -- one where I was almost 100% guaranteed to win because the law was on my side and it was in the hands of one of the best lawyers in town. I had, frankly, forgotten about it because it caused me so little concern. But it gave him something to hang his amateur psychologist diagnosis on. "Aha! I was right!" No, you were wrong, but there's no way to prove that I was not worried about it in the least.
Since he didn't want to accept my cause/effect that this debility related to a flu-like illness I'd had months earlier, he had to find his own cause/effect and kept coming up with new reasons until he finally found one that actually existed, however peripherally.