Hearing a herd of horses

When doctors diagnose an illness they are supposed to go for the most likely diagnosis and not the one that is out of the ordinary for the symptoms. They have a sentence for that: "When you hear a herd of horses, think horses, not zebras." Derived from that is another term "zebra retreat;" that is used for a doctor who is afraid to contemplate the unusual diagnosis. Now I have heard it all! I am sure that doctors always go for the typical diagnosis when they see symptoms. But it seems to me that they rarely go into "zebra retreat" because they don't have the time to think of the extraordinary. There is too little time to think and really understand a situation that lends itself to thinking in terms of "zebras." Doctors also don't want to be sued. So they never even contemplate the "zebra" even if they know that "zebras" exist. It's the safe thing to do call them all horses, even if they see only "zebras." Wouldn't it be best to call "zebras" by their names and have the courage that a sick patient is do?