"I laughed at Xia Chan's endless childhood dreams, and he said that the street lamp couldn't shine tomorrow." This sentence uses metaphor and contrast to describe two situations. "Xia Chan can't finish singing childhood dreams" describes the protagonist's pursuit of happiness, vitality and enthusiasm for ideals and longings in his youth. "He said that street lamps can't shine tomorrow" means that someone mentioned or thought that the existence of "street lamps" can only shine in the present and be eclipsed in the future.