Hi, sorry for the jargon. It's based on a few things I've read while studying psychology and reading about empathy.

One theory is that empathy is split into two parts. Emotional (to do with understanding the feelings of others) and cognitive (which involves understanding what other people are thinking and their beliefs: all the non emotional stuff).

Some argue that emotional empathy is high in people with BPD. We are extremely sensitive to how other people are feeling and look for emotional signs to see whether they're angry or sad etc. We may not be so good at accurately understanding why they feel that way (which is the cognitive bit) but we know how it feels and if anything we care too much.

Cognitive empathy is the part of empathy that deals with understanding what people are thinking and why and is less intuitive for some people. People with high cognitive empathy can make good judgments about what other people think and believe in a certain situation but may be oblivious to how they feel or just not care.

It's just a theory but some psychologists believe that BPD is an empathy imbalance. Having too much emotional empathy without such a high level of cognitive empathy to balance it out can lead to a lot of the behaviours associated with BPD.

To someone without BPD it could appear that we lack emotions but the opposite is true and in fact our emotions are too intense and very real.