Patients come to a doctor because they have a problem and want a solution. Doctors are fascinated by problems - especially those which are rare or complex. Differential diagnosis can be one of the most intellectually challenging parts of a doctor's practise - and since most doctors are intelligent, they love "cracking diagnostic conundrums" and interpreting scans and images. However, once the problem has been diagnosed and the disease given a name, many doctors lose interest, because treatment is usually quite cut and dried and not very intellectually stimulating. After all, zebras are fun to talk about while horses are boring.
On the other hand, while some patients are quite happy to be the center of medical attention because they have a complex problem, most just want a solution so they can move on with their life.
A good doctor will spend as much time and energy on crafting a treatment plan for the patient, as he will on creating a plan for a diagnostic workup. This can actually be harder to do, because it requires the doctor to see things from the patient's point of view - and offer advise which the patient is willing to carry out !