It's been stated before but bears repeating: When I offer tools like the ones here, I'm not necessarily implying that each tool (such as Dialogue Deepening Techniques) always should be used. I'm simply supplying some of the tools of Emotioneering.
While adding depth to characters, dialogue, plots, relationships, and game moments might often be an attractive option, making all these facets interesting, including NPC dialogue (whenever possible), is not an option but instead is something to strive for, unless there's a good reason not to do so.
Because so much NPC dialogue either conveys information or prompts player action, the challenge is to make this dialogue interesting and, if appropriate, deep. As we'll see later in this book, by doing Technique Stacking, it's sometimes possible to layer into NPC even more functions, such as having the dialogue tie into a theme in the game or serve symbolic value.
It's also worth nothing that the way a character speaks can, obviously, change as the game progresses. This could relate to a change in the character's Traits, a shift of allegiances, emotional growth, attainment of depth, or other kinds of change.