This is somewhat an elaboration on my post explaining why it is I write romance novels. It is perhaps inaccurate to have said that what interests me most is specifically relationships as opposed to people – but then again, people are defined by their relationships (and with a birthday coming up while living somewhere hundreds to thousands of miles away from most of my friends, I am particularly aware of this fact). Even fleeting relationships, such as those created temporarily as we check out in the grocery store, provide insight into the people involved.
The development of relationships, sexual or otherwise, depends heavily on the personalities of those involved, which in turn are affected by past relationships. At the crux of the matter, then, what interests me is a completely informal knowledge of psychology, created through observation. What is now frequently called "baggage" is actually a history of the evolution of a person's psyche and personality, which induces that person's reactions to social cues and particular situations.
Untangling those motivations and triggers while also being aware of how those past events shape a person (or character) is intrinsic to creating the dynamic characters that inhabit quality fiction. Romance novels specifically allow a writer to examine the underpinnings of the psychology and backgrounds for all sorts of people and how those feed into every type of interaction, as we show realistic characters navigating their relationships, at least one of which is romantic.
That psychology needs not be the apparently stated topic. In fact, it probably shouldn't be, because psychology is like backstory – it needs to be demonstrated, not dumped as an obvious aside, in order to create complete characters with compelling stories. Comments like the following tell us we just might have succeeded in that goal:
"I feel like I learned so much from reading your story about the human psyche!! I really enjoyed it." (From a first reader's notes on my novel)