It means that life is like a dream and everything is illusory. In China's ancient poems, a big dream is used to describe the brevity and impermanence of life. It is also used to describe lofty ideals and ambitions. In modern Chinese, a big dream is often used to describe the same big dream in life, in which everyone seeks his own meaning and value. Generally speaking, the specific meaning of the word "lofty ideal" will change according to different contexts.