> "What is so hard about the concept/metric being applied here that it can't be put into words?"

> Again, I would guess pg doesn't understand it, and so can't quantify it, but trusts that Jessica's correct more often than not. It doesn't seem like pg was even trying to show everyone how to do what Jessica does, just to clarify that she does many things within YC and that she has often been forgotten in the telling of the YC story; explaining that does not require him to explain how it works.

I can have a stab at an explanation here. I'm sort of straddling the border (being a "socially inept" nerd by nature, and having invested considerable amounts of time over the last 15 years in getting better at the "social stuff") and know enough people who are on the other side, and have spoken with them often enough, to have formed some ideas about this.

First, most people who are really good at this tend to be at a stage of unconscious competence. It's not really something you teach to others very frequently, so it's rare to find someone who spends the time to analyse their own analysis of others, which helps explain the "mystery factor" here. As they say, if it takes 10 years to get good at something, it takes another 10 years to get good at teaching it to other people!

In my experience people who get very good at this tend to be (like Jessica is described in this article) people who have a strong discomfort around conflict and/or other people's distress. I don't know what the chicken/egg situation is - which comes first, the sensitivity to other people's distress, or the skill in reading other people's emotional states? Either way, the two combine and lead to someone who spends a lot of time being aware of how people around them are feeling, what they're thinking about, etc, so that they can detect potential conflicts very early and head them off before they cause distress. Like anything else, you get good at what you do a lot, and someone who spends a lot of time thinking about what's going on in other people's heads is, over a few decades, going to naturally develop an incredible (from the outside, almost magical) skill at reading people from what are almost unnoticeable cues like tone of voice, body language, the content of what they say, what they don't say, etc.

Ultimately what this boils down to, imho, is building a model of the other person in your head. Think of your best friend, the one you understand most - you probably have a model of them in your head. You could have a conversation with that model and, if you have known them for a while and are not totally insensitive to people (which is possible... don't beat yourself up about it!) you can probably predict how they would react to a given situation with a fairly high degree of accuracy. Sure, you'll get it wrong from time to time, but you'll get it mostly right. People who are good at this "social stuff" just build those models much, much more rapidly, and much more accurately, than you do, through practice and habit, and they do so constantly throughout the day with everyone they bump into, so they get to practice that over and over again, and keep getting better.

Does this help a little?