To spend a long time training and preparing for a brief but critical moment; years of preparation for a moment of need.
他平时认真学习，积累知识，真是养军千日，用军一时，才在这次竞赛中脱颖而出。
He usually studies diligently and accumulates knowledge, truly embodying 'years of preparation for a moment of need,' which allowed him to stand out in this competition.
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