yàn​zi​xián​ní​lěi​dà​wō

gradual accumulation

燕子衔泥垒大窝 (燕子銜泥壘大窩) yàn​zi​xián​ní​lěi​dà​wō
gradual accumulation
The swallow's nest is built one beakful of mud at a time; used as an idiom to describe how great things are achieved through persistent, small efforts or how many small things add up to a lot (many a little makes a mickle).

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