"It means that the distance from the first floor to the fourth floor is only three years. It means that the uncles and aunts in the cafeteria and the doormen are very married. They can't understand the various seasonal currents and have new horizons. All kinds of posters and photos that were once crazy are sold for a few dollars and a few cents."
Do you still remember the story sung in the song? Sweet and sour memories, shared realizations, never seeing each other again after graduation.