For Zhuangzi, knowledge is relative to the perspectives we have of reality at the moment. This means that we will never know for sure whether what we know at the moment is real or not. It depends on our perspective. He explains this by showing how one day he dreamed that he was a butterfly, at the moment the dream is happening, his knowledge was limited to the butterfly's perspective, when he woke up, he realized that that perspective was not real, because now he had knowledge with his own perspective, however he could not confirm if they were real too, because he could be a butterfly, dreaming that he was a man, at that moment.
With that, Zhuangzi makes a connection with the myth of Plato's cave, showing that our perceptions and the feelings we feel about the environment in which we are inserted are not enough to make us sure of anything.