Why does the author compare what bogle does to someone standing on their head?

This question refers to the text "Balancing Rocks" by Stacy A. Nyikos. The text talks about Sepp Bogle, who is an artist that creates art by balancing rocks on top of each other.

The author compares this type of art to someone standing on their head for several reasons. The author wants to highlight the fact that both acts take a lot of practice. She tells us that it is likely that you will initially fail at both tasks, but that practice will allow you to improve. She also tells us that both acts require balance to be taken into account and the center of gravity of the rocks or the person to be found.

that's conceptually impossible.

if i wrote it, it wouldn't be a 'shakespeare' sonnet.