In what way is it liberation to experience the impermanence of one’s mind? Why is that wisdom? We ordinarily identify the mind as “my” mind, the body as “my” body. When you have a haircut, the hair that ends up on the floor, is that “you”? After you take a bath, what’s left in the bathwater, is that “you”? You may not so willingly admit that these things are you, but they come from your body. Common sense says that we don’t identify these things as “me.” Well, then who are you? Some people may think, “I am my mind,” and this is the crux of contemplating the mind as impermanent. Mind is “me” as a sense of self. Identifying the thinking process as oneself is the source of vexations and suffering. For example, when we identify with the thought of arrogance, this leads to suffering. When we identify with the feelings of jealousy and hatred, these mental states will lead to suffering.
From Things Pertaining to Bodhi: The Thirty-seven Aids to Enlightenment by Chan Master Sheng Yen, page 19