Althea is nostalgic, and all children who have experienced the pain of youth are nostalgic. They look back at their time of betrayal and despair all the time. The same goes for Jian Xi, and so does everyone in the story. Whenever they think of the scars in the past, they feel extremely heartbroken, and feel like they want to cry and fall into the once black and bottomless abyss of ten thousand years. The past cannot be missed, because when we miss it, everyone will feel the feeling of falling.