A mixture of observation and reading. And it’s not the ultimate definition, a number of other elements could be included as well. But I think these three will be enough to get the basic job done.
One of the big culprits in many interpersonal problems is Projection: our natural (and often healthy and useful) tendency to take bits and pieces of our internal process and to experience them as originating from people and situations outside of us.
Projection serves important functions (e.g., helping us to feel connected to the world and to people), but it can also lead to fatalism (e.g., self-fulfilling prophecies), powerlessness, and ineffectiveness in dealing with the actual realities of external conditions.
So, it’s a good idea to get a handle on it. To take responsibility for what our own bodyminds are bringing to the situation and putting on the situation. Not so much fun sometimes. But pays for itself in the long run, I think.
Owning one’s projections is an important part of self-care. Because it comes back to ‘me’ and ‘what I’m doing’. But doing that for a while then leads naturally into ‘Perspective-Taking’ because when I lessen my tendency to treat people and the world as mere extensions of myself, my agendas, and my process, the next logical step is to start getting curious about what really is happening over there.
Boundary-setting skills arise naturally out of increasing familiarity with those other two parts (Self-responsibility and Perspective Taking). They don’t always work perfectly, but in general, once you know and accept someone’s actual nature, without blame but with detail and accuracy, it is then your responsibility to decide how much access to your inner world is appropriate for that person and how intimate that access can be.
If you rescue a wild boar and bring it back to your home, think long and hard before you decide to keep it inside of the house. They’re not being mean or evil when they chew up everything and defecate on all of your floors. They’re just not really built for inside living. On the other hand, if you take them to a spacious, well-appointed natural sanctuary, they’ll be happy and you’ll be happy: Boundary-setting.
(I just saw an unsettlingly huge wild boar the other night while I was hiking. It was about two times the size of the ones I usually see. Thankfully it was about 30 meters away. haha.)