Introversion and extroversion have to be some of the most confusing terms out there. "Introversion" and "introspection" or "nonconfrontational-ism" get used interchangeably. Extroversion is seen as constantly seeking out social situations and introversion is seen as constantly shying away from social situations. Extroversion is seen as being exciting and entertaining while introversion is seen as being a thoughtful observer.
I see introversion and extroversion the same way Carl Jung saw the two concepts: what makes you one or the other is based on how you get your energy. Do you feel energized by being around people or do you feel energized by being alone?
I consider myself a social introvert. I get my energy from being alone, but I crave social situations. I love being out and around people, but I find it incredibly draining. This can attribute to some level of quietness -- when it takes so much energy to talk to people, why would I do small talk? -- but a quiet person isn't necessarily an introvert.
As you can imagine, this is incredibly frustrating. I thrive on being alone -- I can't tell you how many times I've told my husband "I've run out of social" when being out for too long -- but it's not as fulfilling as engaging with a group. Likewise, if I'm out and around people for too long, I become downright antisocial, with no energy to even smile in response to whatever someone is saying.
So it's all about finding that balance, never spending too much time alone and never spending too much time around people. Which is not exactly easy. Sometimes you don't get a choice in whether or not you are around people, whether or not you are alone for extended periods of time. But there still has to be that balance.
I think the only thing more frustrating than a social introvert is an asocial extrovert, who craves being alone but gets their energy being around people. And even then, it's all about the balance. As the hardcore yogis would say, the sthira and the sukha.