Zhouyi BenyiLine statement
Shaking means swift movement. Six at the Top occupies the extreme of Duration and the end of Zhen. When duration reaches its extreme, it lacks constancy; when Zhen reaches its end, movement is excessive.
Moreover, being yielding yin, it cannot hold steadfastly, and dwelling at the top is not its peaceful place; hence it presents the image of 'shaking duration,' and its divination is misfortune.