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To realize too late that one's knowledge is insufficient when it's actually needed.
考试前才发现很多知识点没复习，真是书到用时方恨少。
Only when taking the exam do I realize how many knowledge points I haven't reviewed—truly regretting not studying enough.
Often used to emphasize the importance of lifelong learning and preparation.
Imagine needing a book when you're unprepared—you'd regret not having studied earlier. This visual helps remember the idiom's meaning.
Use this proverb when someone realizes their lack of preparation or knowledge in a critical moment, especially in academic or professional settings.
Originates from the Qing Dynasty scholar 袁枚's work 《随园诗话》. The full phrase was '书到用时方恨少，事非经过不知难,' meaning 'Only when you need knowledge do you regret not studying enough; only through experience do you realize how difficult things are.' It reflects the Confucian emphasis on lifelong learning.
Commonly used in educational or self-reflective contexts to encourage diligent study. Often paired with the second half of the original phrase about experiencing difficulties.