Accurate answer-it's hard to go: the author uses the metaphor of "water" to describe people. The water flowing in different directions "East, West, North and South" only compares people in different situations in social life. The flow of "water" is caused by topography; People's situation is determined by family status. Therefore, the first two sentences vividly reveal the irrationality of the gate valve system in the real society by describing the common phenomenon of diarrhea.
I hope my friends will adopt it.
thank you