Here is a nice little piece about when and why to distrust expert opinion.
His example about pain reminds me of a great article I found and used in my Media English class (to the befuddlement of student and colleague alike, I'm afraid). Do you remember being taught that the reason your muscles hurt after strenuous exercise was that there was a buildup of lactic acid? Well, it's totally unscientific bullshit.
As I've climbed higher (and really, I'm not that high) on the academic ladder, I've realized something: Experts are just people. They work hard, but they can make mistakes, and they actually have more important things to do than be right. They usually have to eat, and admitting everything you've said for your entire career is bunk can be very hard to do.