is a metaphor for studying hard.

Digging through the wall for light

It comes from the story of Kuang Heng, a great writer in the Western Han Dynasty, who dug through the wall to attract his neighbors to read by candlelight when he was young, and eventually became a generation of writers. Now it is used to describe people who are poor and study hard.

learning without thinking is useless, and thinking without learning is dangerous.

It means that if you read blindly without thinking, you will not be able to use the knowledge of books reasonably and effectively because you can't deeply understand the meaning of books, and even get confused. And if you just dream and don't really study and study, you will eventually build a tower on the sand and get nothing. It warns us that only by combining learning with thinking can we learn practical and useful knowledge, otherwise it will have little effect.