I’m smiling, shaking your hand. “Yes, this was a very productive conversation! I’m sure glad I met up with you and we had this discussion!”
You think I’m going to help support you in your efforts to do whatever you’re going to do with the ideas or information you’ve shared with me tonight. Instead, I’m going to report it to another group that will stop you from doing what you want, take your ideas, or exploit the information in a way counter to your goals.
I’ve just lied by breaking the maxim of Manner.
[Edit: It’s arguable that breaking Quantity would also cover this—I didn’t say WHY it was productive—but it seems clear to me that it’s essentially a violation of Manner.]
I would imagine that’s not a case of stupidity, but of the brain working in a way that’s (usually, more or less) efficient. Instead of analyzing the specific words you’re using, the nurse, who has no reason not to trust you, analyzes the content of what you’re saying, the urgency and manner with which you’re presenting the evidence against this chemical that’s just “blahblahblah” to the brain.
This is a way of filtering out irrelevant content and only paying attention to what is (likely) to be relevant. I had a related problem when learning to drive—my brain doesn’t instantly process “right” or “left” as belonging to the specified direction, but when the instructor or person giving the test bellowed a word at me, I knew to turn and turned whichever way made more sense to me in context—which wasn’t always the right decision. I don’t think everyone has this thinking style, as evidenced by my instructor’s irritation with me, but it’s certainly not overall a bad one—in general, it’s probably better to pay attention to information from the environment when operating heavy machinery, to the emotional content of a social situation rather than to etymological clues, and so on.