Many people even intentionally sharing their data. But you do not even need to provide your data to let Facebook know more about you. I heard that Facebook is "following" you through cookies, even if you are not logged in on Facebook. They can record and study your browsing history, your habits, your preferences. A lot of things. And the AI (Artificial Intelligence) can build a huge and very detailed database about you. Maybe even about things, which even you do not think about at the moment. This is scary to think about.