As I've gotten older, I seem to have developed a very, very shallow arch in my feet. I don't have a lot of childhood memories, at least of which I'm aware, but one is being at some boardwalk on the Jersey shore, stopping to rest with mom and grams, looking at my feet and they were solid black. The memory is probably corrupted, but I have little down that both feet were evenly dark across each sole.
That was about 50 years ago.
I've not really checked since then, so this discovery was . . . let's say, unexpected.
Of course I'm pleased and while unexpected, there was a somewhat logical reason. I can feel my arches touching the ground when walking. What I don't feel, at least not such that it rises to the level of consciousness (unless I inquire), is the difference in pressure.
Hence the description as "a very, very shallow arch."