Mountain birds and fish have different paths. What does it mean that mountains and rivers will never meet again?

Never meet again in the mountains and rivers means that people who like each other will never see each other again. This shows an attitude and a determination.

The mountains stand there, and birds take pleasure in living in the mountains and forests; the water flows quietly there, and the fish live freely in it. Birds and fish are not fellow travelers. They live in different environments, have different living habits, hobbies, and ambitions. Therefore, just like mountains and rivers that cannot meet, they cannot live together.

This sentence actually expresses one's attitude towards feelings. Tell each other clearly: We are not on the same road. You have your pursuits and ideals, and I have my ambitions and hobbies. Although we meet, we will not have like-minded pursuits, so just forget about each other.

The birds in the mountains and the fish in the water are not the same kind of animals, so fish and birds cannot meet. Even if they meet, it still feels like they are destined but not meant to be together.