What does the idiom eye mean?

The "eye" in the idiom "one board at a time" refers to the beat, and the strong and weak beats in China traditional music are represented by "board" and "eye" respectively. "Board" is a strong beat and "eye" is a weak beat, both of which are 1/4 beats. So "one board with one eye" is 2/4 beat, and "one board with three eyes" is 4/4 beat. Later, it also refers to things that are rigid, such as 4\4 beats.

Idiom explanation:

In China traditional music, the strong beat and weak beat are represented by "board" and "eye" respectively. The board is strong beat and the eyes are weak beat, both of which are 1/4 beat. So "one board with one eye" is 2/4 beat, and "one board with three eyes" is 4/4 beat. Later, it also refers to things that are rigid, such as 4\4 beats.

This meaning was later extended. Metaphor words and actions are organized and conform to the rules. Sometimes it is also a metaphor for being rigid and not knowing how to master flexibly. Same as "one board with three eyes"

Extension: Metaphorical words and actions are organized and conform to the rules.

Source: Wu Gone with the Times: "The current situation is that Confucius is alive and doing nothing, but he is actually just a nerd."