 The rules of politeness are built into the language, and you learn them as part of the language, which, again, is part of the culture that it's attached to. I'm thinking of this structure that you're talking about, making a statement and then saying, but. That's one variety of it. There are also softeners like starting a sentence with, all I know is da-da-da-da. So you're discounting your own expertise in order to make the other person know that you don't believe yourself to be arrogant and all-knowing. Right. Uh-huh.