Hi I don't post much anymore, but sometimes read, and this caught my eye - you might want to look at some of Dorothy Rowe's writing on extroversion and introversion [Australian therapist who has worked in the US and UK e.g. 'The successful self]. Her theory is that introversion and extroversion are to do with our brain structure, and that introverts need to develop their extrovert side, and viceversa to become mature and fully functioning people. Also introvert/extroverts make good partnerships.
