If the symptoms are 30% similar to a disease that 99.999% more common, and 70% similar to a disease that's 0.001% common, the doctor would still be correct most of the time by suggesting that the patient had the common disease, even though the symptoms were a better match to the rare disease.
If the symptoms are 30% similar to a disease that 99.999% more common, and 70% similar to a disease that's 0.001% common, the doctor would still be correct most of the time by suggesting that the patient had the common disease, even though the symptoms were a better match to the rare disease.