be not to know
idiomPart ofknow
be not to know — idiom
1. Used to say that someone had no way of realizing they did something wrong.
1.idiom
Definition
Used to say that someone had no way of realizing they did something wrong.
Example
Don't blame him for the mistake; he was not to know.
I'm sorry I broke the vase. You weren't to know it was fragile.