This sentence expresses the deep feeling of missing someone by depicting the scene of alternating autumn and winter and the way that missing quietly enters the dream. Autumn is a season symbolizing parting and withering, and winter represents cold and loneliness. By comparing the missing with the fallen leaves in autumn, it implies the intensity and persistence of missing. The feeling of missing someone, like the fallen leaves in autumn, quietly enters the dream, and the feeling of missing someone in autumn and winter is stronger.