From artist Grant Snider of Incidental Comics:
Humans are social animals, and that includes introverts. But we're sort of like camels or deep-diving whales, in that we can go without this thing we need to survive for longer periods than others can, and seem to prefer it. We're more adapted to it. We don't necessarily dislike being around other people, but if it's for a sustained period we can feel drained afterward, even if it was a fun time spent with friends. The benefit is in not being lonely when a more extroverted person might be climbing the walls. The detriment is being assumed anti-social and/or missing out on opportunities that more outgoing people often receive. But you know what? I can't imagine being any other way.