They are trusted by most, since they are willing to listen and because they know how to keep secrets.
Consequently, they know secrets.
Quiet people are often dismissed, but they can easily destroy the babblers, who love to talk and share, including their secrets.
Quiet people are usually also wonderful observers. They notice the details, they study every tone, every gesture.
Before one knows it, one's at the mercy of the quiet.
You'd be wise to respect the quiet.