I am interested in reading Cain's book. I have scored solidly in the "I" range on two official MBTI assessments that I have taken. But I am a very chatty person, to the point that my husband has learned to tune me out at times. Where does this leave me? I am an enigma.
Naw, that makes you me.
(I will say that I tone down the chattiness on campus visits, haha.)
Don't do that as a general rule; make your ability to be changeable work to your advantage. In places where people are looking for chatty based on contextual clues, I am chatty, bubbly, and vivacious--sure, let's have dinner three hours past my bedtime even with an 8 am teaching demo because I love to meet people in a more casual setting.
However, in places where the password is friendly, but somewhat independent, sure, I can entertain myself for an hour break, thanks for the downtime to reflect and maybe pull out some reading; I even have time to go look at some bulletin boards in other departments.
Be the best you that fits with the local culture and you will do well. A caveat is to make that best you be you. You will be miserable if you set yourself up as bubbly and vivacious when you will be extremely reserved and quiet as a daily behavior.