Temperament – What’s Real?

I’ve studied temperament and personality now for over 10 years. I know the natural strengths and weaknesses of all kinds and types of people. But the saddest thing I think is a person who, for who for one reason or another, has “put on” the behaviors of a temperament type not their own for such a long time that they have “become” that type. It seems so forced and unnatural, like an introvert who thought they had to be outgoing so they forced an outgoing “face” for so long that it stuck (Like your mother told you – if you keep doing that your face will stick that way!) What are your experiences with people who behave “off type”?