平薄之別

In English, 平 and 厚 is related, such as in the word slab, which means 平 and 厚, slab's opposite is 薄, thin slice. This may symbolize current power struggle between Xi and Bo.

Well, think about stock trading, you want to be 平厚 or 薄 ?

Why thin is related to rough? just think that a thin board will easyly get warped (qiao4).