a.k.a. Battle of the Verts.
In one corner, we have the Extroverts. Extraversion is "the act, state, or habit of being predominantly concerned with and obtaining gratification from what is outside the self". Extroverts enjoy human interaction; they are gregarious, aggressive, enthusiastic, and talkative. They are energized when spending time with other people and tend towards boredom when left to their own devices.
In the opposite corner, we have the Introverts. Introversion is "the state of or tendency toward being wholly or predominantly concerned with and interested in one's own mental life". Introverts are energized through reflection and sapped by interaction. They tend to be more reserved and less outspoken than their counterparts.
So, which are you? Chances are that you are an introvert, as the archetypical artist – and we writers are, indeed, artists – is highly introverted. The bigger question is, can you write extroverted characters? Or do you let your own biases sneak in where they don't belong?
Let's say you have a character who is a teacher. Does she come home exhausted every day, eager to lose herself in a little Jane Austen and a glass of wine? Then you'd better not make her the life of the party at her sister's wedding. But that scene is critical to your story, you say. Easy fix – she becomes more dynamic in the classroom, maybe offering after-school tutoring or mentoring a club.
How do you create characters that are alien to you? What are your strategies?