The first step is to examine materialistic knowledge.
The second step, "The most important thing is that the world can't stay, Zhu Yan's words in the mirror, flowers on the tree" means that many things in this world are hard to stay, just like the face of youth is getting old and can't bear to look in the mirror. When flowers rot, they will fall off the branches. Here, we use "Zhu Yan's flowers under the moon in the mirror" to describe that the beautiful things in the world are always so short-lived, as if they would disappear at any time. This sentence shows that time is linear and irreversible, which embodies the one-dimensional nature of time.