I think there is a difference between reading body language accurately and imagining how you yourself would feel in a given situation.
I think, for me personally, I learned to read body language really well because of growing up in such a dysfunctional family. Like any other skill, it can be learned if you have enough time and motivation to practice.
And I think that, when seeing situations similar to something I've experienced before, I can easily (maybe too easily) imagine what
I would feel like in that situation.
My problem, though, is knowing what
another person feels like in that situation, because it seems to be so different from me. And then I don't know how to respond to that person because what they need is different than what I would need in the same situation.
I've learned rules and patterns of how to respond, based on decades of observation. But it's just following rules...it's not responding from an intuitive understanding of what that person is experiencing. It's all a cognitive process, which doesn't always produce the appropriate response to the person, resulting in hurt feelings and offended reactivity.
For example...I know someone whose grandfather just passed away. I told her I was sorry for her loss. I know from studying people and the grief process that this is an appropriately supportive thing to say. So I said it because I hope that's helpful for her, but not because I would want someone to say that to me in the same situation.
When my grandmother passes away, I think I'll be glad for her. She's very old, and has always said she didn't want to live long enough to lose her mind and be completely dependent on people. Lately she's started losing some of her grip on reality, so I really think it would be a relief to her to go before she is completely senile. This is what she has said for many years, so I believe her. When she goes, it seems like I would rather hear from people things like, "Your grandmother was such a beautiful person--I'm so glad she got to live such a satisfying life with so many family members who love her so much." (From people who didn't know her, I guess I don't know what I would want them to say.)
But I now realize that what I want is fundamentally different from what other people want and expect. So I have to study them to figure out those differences. And I now am trying to understand myself better, too, to figure out what I actually need, rather than trying to get the things I thought I needed simply because that's what people said are supposed to help in various situations.