[anigbrowl]

Continue by trying to touch two fingers on opposite hands behind your head. Why can't you do that?

I can, easily, every time, any pair of fingers, and also behind my back and many other positions. Really, I don't care for this assumptive style of explication.

I can readily believe it is an issue for many or even most people (you have investigated and know far more about this topic than I). I am able to do this from a combination of spacing out on this sort of thing since childhood and a lot of athletic training, but surely this isn't that rare.