An extraordinarily important article. I quote it:

Do you know someone who needs hours alone every day? Who loves quiet conversations about feelings or ideas, and can give a dynamite presentation to a big audience, but seems awkward in groups and maladroit at small talk? Who has to be dragged to parties and then needs the rest of the day to recuperate? Who growls or scowls or grunts or winces when accosted with pleasantries by people who are just trying to be nice?

If so, do you tell this person he is "too serious," or ask if he is okay? Regard him as aloof, arrogant, rude? Redouble your efforts to draw him out?

If you answered yes to these questions, chances are that you have an introvert on your hands—and that you aren't caring for him properly.