5 Centimeters Per Second: What does the ending mean? In 5 Centimeters Per Second, a boy and a girl get separated, and then try to meet with each other.

In the ending, when they are grown up


   The boy sees the girl as they are crossing the train tracks. They are interrupted by trains. The boy waits for the girl, but when the trains pass, she is gone.


Why is that?
I attribute this to what would best be called a "Fleeting moment and feeling". His desire to see the girl again caused him to envision her being there for a moment which is personified by the passing train (another symbol that life moves on). But when it passes, so does his desire and like the train, he decides to move forward with his life.