Hickam’s dictum is a counterargument to the use of Occam’s razor in the medical profession.
The reason for using Hickam’s dictum as a limiting principle to that of Occam’s razor is that it is often statistically more likely that a patient has several common diseases rather than having a single, rarer disease that explains his myriad symptoms. Another key reason is that, independent of statistical likelihood, some patients do in fact turn out to have multiple diseases.
As a paramedic, I have often treated a patient who’s signs and symptoms do not match any given single condition. Later, it has been determined that the patient has had multiple ailments and not one large bizaire medical condition.