Is Small Fear of Uncertainty the defining Attribute of an Extrovert?

I prefer cerebral introverts for any activity that involves brain cells. So take my words in the context of an ally who likes accurate descriptions of reality. Most of you are introverts. To be more precise, most of you are power-, status-hungry, introverted software yuppies (I've been one, no shame in it:) What would you say is the defining characteristic of an extrovert? I think we all read what Paul Graham had to say, so let's not rehash that. What do you think defines an extrovert?