I know a few doctors and the vast, vast majority of patients have what you thought they had when they walked in the door. Boring, could-have-guessed illnesses (or maybe not).

99 times out a 100, if the doctor thinks it's something else, it's not.

So when someone comes in who doesn't fit that mold, they get shuttled around to a bunch of doctors until it gets bad enough someone is forced to think outside the box.