In our family, we've sort of made a parlor game out of Myers-Briggs - trying to figure out what type various real people and characters are. We don't ever assume we've gotten them right, though.
I realized, recently, that we don't usually try to type people from different countries or people who died a while ago. C.S. Lewis is both.
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There is so much more that goes into one aspect of behavior, such as letter writing, than just a Myers-Briggs type. I know a very diligent, and extremely charming, E/INFP letter writer. For her, ...