Do you remember the pie chart of all knowledge? The circle, the pie, represents all facts in the universe?
A tiny slice you know and you know that you know it. It is your address, it is your name, it is facts that you can prove.
Another tiny slice is all the things you know that you don’t know. For example you know that you don’t speak Japanese, unless, of course, you do.
The rest of the pie is the things that you don’t know that you don’t know. Some of it you think you know, but what you think is just isn’t so.