All in your head

This is based on a note to myself from a couple of weeks ago.  I was at the UU Sangha I attend, and the Dharma lesson for the evening included an exercise: first, cultivate a generalized feeling of loving-kindness in yourself; then, picture the face of someone you have trouble with and try to feel the same loving-kindness towards him or her.

One of the other members said that while she was able to call up a generalized sense of loving-kindness, as soon as she pictured the face of That Person she could feel herself constricting and closing in.  What's more, she went on, she could feel a sense of active resistance or even hostility emanating from That Person towards her.  I agreed with her that it was very easy for me to feel the exact same thing, but then asked a question: Isn't it interesting that you -- or I, or anybody -- can feel active resistance from That Person when in reality That Person isn't even there?  He's just a picture in our minds, that we deliberately imagined for the sake of the exercise!

What does this mean?  Clearly what it has to mean is that any resistance we are feeling from That Person is something we are imagining along with imagining his face.  It's all in our heads.  And that idea, naturally, raises the question: how much of the resistance or negativity that we feel from someone else in real life is also just all in our heads?

I don't have a clear answer.
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For whatever it is worth, I find I still have a lot of arguments in my head the way I used to; only now they are no longer arguments with Wife, but with my father.  Maybe there aren't quite as many, actually.