In theory these are default states - if external factors are removed, what would you revert to?

I default to INTP but can ramp up the E as needed (and these days I need it more an more). I can mess with the other values too, but I/E is the easiest for me to play with.

I/E isn't as much about whether you are "outgoing" or "gregarious", etc. It's really more about whether you:

* Process things internally/externally * Get energy from being with people or find being with people "draining"

I'm also an I who has learned socially acceptable things like public speaking, participating in group discussions, etc. but a couple of hours in such a group and I'm exhausted while my E wife is energized.

Precisely. I'm an Introvert but I can do things like public speaking, having a job interview or giving a lecture reasonably well. Also, I have no trouble to get into a circle of strangers and easily initiate a conversation - as long, of course, it is some kind of interaction where I think it is meaningful. But after some time interacting with people, I just want to go home, get back to the computer, a book, swim for an hour by myself, etc.

On the other hand, I have a friend who is an Extrovert, but at the same time he is considerably shy. He craves interaction and is really cool with people that he knows, but it seems that he blocks whenever there is someone new in the room, or in a situation where people might judge him.