Lower Extraversion is not the same as shy, unfriendly, or lacking confidence. People lower on this trait often notice the room before entering it: who is engaged, what the conversation needs, and whether their contribution would improve it. They may prefer one considered observation to five improvised ones, not because they have less to say, but because their thinking often becomes clearer before it becomes public.
Company can be welcome in the right dose. After a day of meetings, conversation, and demands for attention, an evening with a book—or simply no one asking anything—can restore more than another enjoyable outing would. The cost of this strength is that others may read reserve as disinterest, or that a good idea may remain invisible because it was never voiced. Naming your preference for preparation, and making a point of entering the conversation when it matters, helps people experience your quiet as intention rather than distance.