In the Book of Songs, there was a phrase that meant " not what I want to exist." This sentence came from Zhou Nan·Han Guang. It was a poem that expressed the feelings of longing. Among them,"Si" referred to the feeling of longing and nostalgia, while "Cun" referred to existence and survival. Therefore," I don't want to exist " could be understood as " not what I want to exist ", which meant that the person or thing I miss does not exist as I originally imagined. This sentence was often used to express nostalgia for someone or something. It was also a kind of dissatisfaction with reality and nostalgia for good memories.