Need to know rule

Bernard Woolley: But, you only need to know things on a need-to-know basis.

Sir Humphrey Appleby: I need to know *everything*. How else can I judge whether or not I need to know it?

Bernard Woolley: So that means you need to know things even when you don't need to know them. You need to know them not because you need to know them but because you need to know whether or not you need to know. If you don't need to know, you still need to know so that you know that there is no need to know.

Sir Humphrey Appleby: Yes!

Bernard Woolley: Good. That's very clear!

From the “Yes Prime Minister” sitcom