Once Zhuangzi dreamt he was a butterfly, a butterfly flitting and fluttering around, happy with himself and doing as he pleased.
He didn't know he was Zhuangzi.
Suddenly he woke up and there he was, solid and unmistakable Zhuangzi.
But he didn't know if he was Zhuangzi who had dreamt he was a butterfly, or a butterfly dreaming he was Zhuangzi.
Between Zhuangzi and a butterfly there must be some distinction!
This is called the Transformation of Things.