In a society where you aren't really supposed to say what you're thinking—witness all the trouble Lydia gets into—it's no easy task to express feelings, correct mistakes, and give context for your decisions and actions. It's basically the early nineteenth-century equivalent of being required to communicate via vague Facebook statuses. In Pride and Prejudice, good manners and the rules of acceptable behavior tend to be obstacles that get in the way of meaningful discussion. But breaking these rules carries its own dangers. Only the characters who manage to walk the line between frankness and bluntness are the ones who get the narrator's grudging approval.
A lot of the novel's humor comes from the way characters are totally unable to understand each other or to make themselves understood.
The most powerful characters are able to shut others up when necessary.