It means: because everyone is an independent individual, everyone has his own interests and demands, material needs and spiritual and emotional needs.
People, of course, must manage their emotions first, and it is certainly better to have a good mood. He has no reason and no obligation to pay attention to those people across the street, and naturally he is unwilling and difficult to understand the joys and sorrows of those people across the street. The noise across the street affected his mood, making it difficult for him to keep a good mood, so he felt very noisy.
The original source of this poem:
There is a passage in Lu Xun's "A Collection of Little Miscellaneous Feelings": "A person downstairs is critically ill, and the family next door is singing a phonograph, and the opposite is a child. There are two people upstairs laughing wildly; There was also the sound of playing cards. A woman was crying for her dead mother on a boat in the river. The joys and sorrows of human beings are not connected. I just think they are noisy. "
We have no time to care about the joys and sorrows of others, and few people care about our joys and sorrows. Even our happiness is the sorrow of others, or our sorrow is the happiness of others, and there is no empathy in the world.