We go to the doctor because we want to know what's wrong with us, and get it fixed. The doctor can usually figure it out... unless she can't.
MDs and other medical pros are humans, not gods. And the difficulty of figuring out what's what is exemplified by the title of Dr. Steven Hatch's book: Snowball in a Blizzard.
He teaches at a medical school and urges doctors to admit that they are stumped, if and when they are. This is a repeat interview from 2016.