Let me emphasize in a UNIQUE dialogue. As an Objective, that means I have to come away with learning something new about the PCs or Players. Something material to add to my notebook and game notes. Its discovering a New thing to Appreciate about the Players.
Particularly something Unpredictable! This metric is challenging if I am able to control or limit my expectations and when I am reeling from the stunning effect of my expectations being bypassed and I have to work to catch up.
Unique Dialogue vs Conversation. Dialogue means really LISTENING. Often used by manipulative people to frame a situation, falsely, as a way to cause *Unilateral (One sided) Change vs *BiLateral (Both Sides) Change.
*I find them "Big Words" and Jargon used to confuse people.
In any point in the GM session, I should be asking myself - Did I learn something new?