Right, and attempting to do a Fermi estimate and then checking it would help you see that that was something you didn't know. (Maybe I'm not getting my point across well here. My point wasn't that such a Fermi estimate would have been in any way accurate. My point is that identifying what made it inaccurate would have helped you update more.)
Ah, I see. I'll try and bear that in mind next time I go looking for info like that!
There's a lot of background mess in our mental pictures of the world. We try and be accurate on important issues, but a whole lot of the less important stuff we pick up from the media, the movies, and random impressions. And once these impressions are in our mental pictures, they just don't go away - until we find a fact that causes us to say "huh", and reassess.
Here are three facts that have caused that "huh" in me, recently, and completely rearranged minor parts of my mental map. I'm sharing them here, because that experience is a valuable one.