Chinese philosopher (Zhuangzi)'s Butterfly Dream where he dreams of being a butterfly and after waking up, questions if he was a man dreaming of being a butterfly or if he was a butterfly dreaming of being a man. The idea is that we cannot be 100% certain about anything (even our reality and existence).

the reality he feels is fragile and fleeting, like something that appears and disappears easily.

存在-胡蝶の夢-