Very interesting story. The length of all blood vessels in the human body is often (incorrectly) listed as 100,000km, because of a back of the napkin math calculation from 1922.

A more recent study shows that it is probably only about 9,000-19,000km.

This is a problem I hear about a lot with research papers, where people use “common” baseline facts not realizing they were either incorrect, or never actually studied. Someone could probably spend their whole career just doing research and fixing data around common sense factoids in their field.