“How can I let the introvert in my life know that I support him and respect his choice?
First, recognize that it’s not a choice. It’s not a lifestyle. It’s an orientation.
Second, when you see an introvert lost in thought, don’t say “What’s the matter?” or “Are you all right?”
Third, don’t say anything else, either.”
Jonathan Rauch. Caring for Your Introvert, article at The Atlantic.