It is taught in medical schools to suggest to medical students that they might best order tests in that sequence which is most likely to result in a quick diagnosis, hence treatment, while minimizing unnecessary costs.
It is applicable to any process of diagnosis, e.g. debugging computer programs.
A more thorough analysis will consider the false positive rate of the test and the possibility that a less likely diagnosis might have more serious consequences.
The law can also be applied in prioritizing tests when resources are limited, so a test for a treatable condition should be performed before an equally probable but less treatable condition.
"[2] A similar idea is contained in the physician's adage, "When you hear hoofbeats, think horses, not zebras."