My favorite example of conventional ignorance: some guy was traveling on a plane the girl sitting next to him asked him whether there was wifi available so she could browse the internet. This was about 20 years ago... and the guy was convinced that the girl was an idiot. "We were flying in the middle of nowhere, 20000 feet in the air, and this girl is asking me whether we have wifi?? Some people have no common sense!" Turns out there's a fine line between being an idiot and being ahead of your time.