JF Ptak Science Books Quick Post
The part about The History of Obviousness that is so wonderful is that sometimes the obviousnesses aren't evident, or apparent, until they are established--and then of course there is no ghostly memory of their formative semi-hidden natures. Sometimes things are best hidden in plain sight, and sometimes one doesn't realize that is is raining men-in-bowler-hats until Rene Magritte points it out. This may be one of those cases where something is so obvious that its extreme nature just blends into the surroundings, even when there aren't any.
[Source: Illustrirte Zeitung, December 31, 1914.]
So, in the picture above, we have not only a guard/observation station built in a lonely tree, but there's also a small lean-to at the bottom, with of course a soldier standing next to (but not inside) it.