Sink-and-board Shadow Play Episode 7: Han Xin's Divination Words.

The board against the wall turned up and down.

Interpretation: Metaphorical things always develop and change.

Source: The "wooden rafters" used for retaining soil in ancient times were called "boards" (formwork and plywood). During the operation, stakes are erected to fix the boards, mixed soil is placed in the middle of the boards, compacted and rolled flat, and a layer of boards is compacted (also called laying a layer of boards), and then the lower boards are replaced with the upper ones. This cycle is what the folks call "the boards hitting the wall are turned up and down".