10 years ago, it was the work of Carl Jung, via the book The Manticore by Robertson Davies.
This time around, the discovery is Attachment Theory.
It was originally developed around infant and child psychology to characterize the way children related to their primary caregiver(s) (and some unfortunate "therapies" emerged in its name), but about 30 years ago, some geniuses decided to extend it and apply similar concepts to adult romantic relationships. I think they got it pretty dead on.
Attachment theories applied to adult relationships
If you, as I have, find yourself repeatedly enmeshed in romantic relationships that become unsatisfying (or even start that way), you may be fascinated by the descriptions of attachment styles in adult relationships and seeing where you and your partner(s) fit in.
For instance, in my relationships, I tend to model a pretty perfect anxious-preoccupied attachment style, and the lasses with whom I most often hook up tend to fit the fearful-avoidant model.
In my last relationship, holy shit was it ever that way, especially in the last couple of years.
I am particularly interested in therapies that are based on Adult Attachment Theory. I found a therapist with training in one flavor, Accelerated Experiential-Dynamic Psychotherapy, and will be starting with him on Monday evening.