Come on, dude. I'm really disappointed with a potential future doctor writing something like that. That sort of reaction is unwarranted. There is a lot of truth in what limeuu said. If you follow ward rounds in the hospitals you will realize that common diseases ARE far more important than rarer ones(from a doctor's point of view). Not because patients with these diseases are less deserving than those with more common diseases, but because you're going to be managing them far more frequently! There is a saying in medicine: "Common things occur commonly".

It is IMPOSSIBLE for a doctor to be able to achieve a right initial diagnosis ALL the time. We are all human, and try as we might, there are limits to our abilities. So yes, to a certain extent, missing an extremely rare diagnosis does absolve you from blame...the same way you wouldn't expect a single electrical engineer to explain ALL the details of say Core 2 Duo microprocessor design and operation(they have many teams of engineers working together to make things happen). However, missing a common diagnosis is far less excusable, especially with a fairly classic presentation. If you're in clinic and see a young Malaysian child with fever, shortness of breath and a productive cough would you consider infectious causes first or would you order a high-resolution CT of the thorax to rule out any microsopic lung cancer(NB:extremely unlikely!). Missing a diagnosis of early lung cancer(by not performing a high resolution CT, which by the way, exposes a patient to radiation risk) in such a case would be understandable....but missing pneumonia would not.

Some diseases are so rare that an average doctor might never see them in their lifetimes. If you apply the standard of "a doctor must be able to diagnose all dieseases, even extremely rare ones"....then i'm afraid no one would qualify to practice medicine.

We study to provide the best level of care to as many people as possible. And because our resources like time an energy are limited, we choose to devote more of them to common diseases. You write as if we live in an ideal world where doctors are all-knowing and infallible. Well, wake up kid. We're not!