Well, when you need to go to an emergency room, you can't really shop around.
Say you get hit in the head, or have a stroke or heart attack, or you've cut yourself and you're bleeding heavily.
You want to go to the nearest emergency room as soon as you can. You can't really do comparison shopping.
Or if you go to Dr. A, he gives you one diagnosis. Then do you go to Dr. B and get another diagnosis? And if they are different, do you pay for the one you don't want?
Examples of this are:
- Sunburn vs. skin cancer;
- A bad cough from bronchitis vs. lung cancer.