Someone can write lots of paragraphs on this Kafka/river analogy (just one random example), but that doesn't impart in my head the same neuronal linkage that they have. Instead I am left, like the post author, trying to figure out how far the analogy extends, what the limits are (okay, so messages are like notes-in-bottles dropped in the river... but what are the fish? are there fish?), and so on. I would rather get clear, detailed explanation, and then think through the subject on my own time in a way that allows my brain to build its own relationships with the information. Maybe instead of rivers, my brain begins to understand Kafka as, I don't know, highways.
I can see your point, that if you try to "steal" the analogy (in the Picassian sense of the word), the analogy could become more distracting than helpful. If you take it for what it is and try to focus on the author's or speaker's vision, they probably work much better.
To someone reading in Europe, explaining something by analogy to baseball innings, bases and pitchers reads: "think of it like dipping your youtiao in chashaojiang instead of haoyou"