It means: mountains and rivers are never like the four seasons, and the ups and downs of the years follow the fate, and they are not forced or changed. It means that when you are alive, you are never allowed to make too many vows. Let nature take its course and let fate come.

Mountains and rivers do not swear the four seasons, but rise and fall with the fate. When our fate comes, we will take good care of it and prevent it from being covered with dust. When it's gone, we won't stay too long, bless each other deeply, and everything will go with the flow.