I found a blog about introverts the other day, probably linked somewhere when I was going through Google Reader. Very very interesting--"It'll be fun!" and other extrovert lies made me laugh out loud because of my initial urge to counter with "But it's true, it will be fun!"
Introversion has caused me confusion my entire life, largely because I grew up in a family with two people that are extremely introverted and suffer from social anxiety, not that they knew this about themselves necessarily or ever explained this. Another thing about people like this is that they can be extremely different in a situation with a few people they know well than around strangers. At home, my dad was gregarious, told stories, made jokes. When he left the house for a reason other than employment (which was rare, most of our errands involved my mom, sis and I), he because a totally different person, quiet and terse. When he was like this at home, it usually meant that he was angry with us, so I spent quite a few years trying to figure out what he was mad about in public before I was old enough to figure out his introversion.
It took me even longer to discover that my sister was the same way. It wasn't until she was 18 and I was 20 that I realized that she was just like my dad in this regard. I'd taken her shopping for some school stuff (we were at the same university, she was just starting out) and we ran into one of her high school classmates in the aisles. This girl had been a cute popular cheerleader type, she was very nice and greeted my sister, tried to be really friendly, and my sister just paused and finally got out a tentative "Hi." In the car I was laying into my sis for this, like "She was being so nice to you! Why were such a bitch back?" Her response was something like "I wasn't sure why she was talking to me, I was confused and put on the spot." Then it clicked and I realized that she was just like Dad.
If it takes you 18 years of living with a sibling to realize how introverted and shy she is when in public, there is definitely need for some introvert education.