This line takes its position above the ruling yang line. While the lower yielding lines find their head in this yang line, the yin line at the top has no head to follow and must therefore go astray
This passage directly names and defines the ruling yang line as the orienting authority of the hexagram, demonstrating that lines which stand above or outside its governance lose structural coherence and fall into misfortune.
, The I Ching or Book of Changes, 1950thesis