High Likeability Dialogue
I've been mad at how poorly understood this system has been myself, and so I decided to finish (sorta finish) my draft for a rework on how this info is presented on the wiki. See NPC Intimacy for the whole of it. Unfortunately, general trends are not 100% true for every NPC but I think this page should help.
Basically, Memory and Favor have to both be high (usually). One or the other isn't enough for what most people consider to be "High Intimacy" (i.e. Secret Shops), although for stuff like Dunbarton NPCs it is true that Memory can affect the first response to Private Story (this is not true for most of the later NPCs because the developers sorta just got lazy in some places). New and old NPCs can have a series of responses to a single Keyword though, including Private Story (which is usually affected by Intimacy) or even sometimes regular Keywords like "Bow".
The biggest takeaway from my research is that Stress decays really fast, that it blocks a lot of the benefits of intimacy, and that it is basically always generated when you first open the conversation journal (which is why checking if you are intimate enough can put you into an endless loop of thinking you're not intimate, gifting, checking again, gifting, and so on).
This is really good, thank you! I have a contribution I will add to the relevant talk page in a moment.
So far my assumption is that the earlier NPCs (G1-3) have a much more... intimate system with their Keywords. Several NPCs of the same era don't really respond to anything, but have a lot of default Private Story responses (looking at you, Chapter 2 and 3.) And then there's Chapter 7... Hoo boy. Lots of Talky, but most of those NPCs don't even accept gifts.
As I'm learning more about the system I think I can more consistently study and record what value affects what keyword response, however I must wait as I have learned 24 hours is not enough time for an NPC's favor to decay naturally. Everyone is still "looking at me with great interest," I will say. Thanks again!