There are known knowns:

there are things we know that we know.

There are known unknowns:

that is to say, there are things that we now know we don’t know.

But there are also unknown unknowns:

there are things we do not know we don’t know.

— Rumsfeld D. (2002) Press Briefing

via Don’t listen to successful people • Intense Minimalism.

PierG