A good moderator is well prepared, has a set of questions in mind for each panelist, and has a good idea of how each panelist will respond to each question. And then the discussion starts and things get interesting. Someone says something that wasn’t expected. They allude to an opinion that doesn’t fit what is usually expected of them, or to a decision that was a mistake. That’s why a moderator’s most important job is to be in the moment and listen — even while thinking about time limitations, who hasn’t gotten to speak yet, and topics that have to be addressed.
Listen for that surprising moment, and follow up on it.