A closed book
Meaning
Someone or something that is difficult to understand, particularly a person whose thoughts or feelings are not easily known.
Origin
Imagine a time before readily available information, when books held immense knowledge yet remained physically imposing objects. An open book invites you into its world, sharing secrets and stories. But a closed book? Its contents are sealed away, its pages unread, its mysteries intact. This simple, universal contrast between revealed and hidden knowledge naturally lent itself to describing anything that was impenetrable or finished. To declare a person 'a closed book' was to say their thoughts and feelings were as inaccessible as the unread words within a sealed cover, their inner world a perpetual enigma.
Examples
- Despite years of working together, I still find my boss to be a closed book; I never know what he's truly thinking.
- Her past was a closed book, and she rarely spoke about her childhood or experiences before moving to the city.