What is the meaning of the idiom "suddenly enlightened"?

Suddenly enlightened _ pronunciation _ interpretation _ study abroad network

[Pinyin]

Hulan circle

[Interpretation]

Suddenly: describe openness; Cheerfulness: Cheerfulness. From dark and narrow to spacious and bright. Metaphor suddenly realized a truth.

[source]

Qian's Peach Blossom Garden: "Only when you are very narrow at first can you understand people. The number of complex lines is ten steps, and it suddenly becomes clear. "

[example]

After the Chinese teacher explained a passage of ancient Chinese word for word, we suddenly understood the meaning of the article.