People have this enormous need to express themselves, but a limited capacity to pay attention to others. So what drives conversation? Obviously attention, because that's scarce.
Conversation is a sequence of ... um, exchanges. And an exchange, for it to be completed, requires acceptance.
Exchanges feed off attention.
In conditions of attention-scarcity, exchanges must compete among themselves for their fodder. This is the classic situation where Darwin's law of natural selection operates. Only the fittest exchanges survive, as determined by their ability to grab attention.
Therefore, conversation does not progress by any intelligent design, in either the sender's or the recipients mind. It is formed automatically by stringing together of exchanges that had the best chance of survival.
That's such a disturbing thought.