Zhuangzi dreamed that he became a butterfly one day. When he woke up, he found that he was still Zhuangzi, so he didn't know whether he dreamed of a butterfly in Zhuangzi or a butterfly in Zhuangzi. Here, Zhuangzi raised a philosophical question-how people know the truth. If dreams are real enough, people have no ability to know that they are dreaming.
This fable is a famous article expressing Zhuangzi's thought of homogeneity. Zhuangzi believes that if people can break the boundaries between life and death, things and me, they will be unhappy. It is light and ethereal, and is often quoted by philosophers and writers.