> Ive met many self declared introverts who have no problem socializing for long periods in small groups with people they trust absolutely.
How do you know they had no problem socializing for long periods? Did you ask them, or did they just not complain about it to you? Part of the issue for many introverts is the social expectation is often set by a more extroverted culture, and they just try to fit in. That doesn't mean they prefer chatting with you for four hours rather than, say, two hours.