I can readily admit that the "everyday Scrabble player" has no idea how incompetent he is, but I don't think that Scrabble provides an example of the unknown unknowns. An unknown unknown is not something like the word "ctenoid," a difficult word by most accounts, or any other obscure, difficult word. ... Surely, the everyday Scrabble player knows that there are words he doesn't know. Rumsfeld could have known about the gaps in his intelligence information. How are his unknown unknowns different from plain-old-vanilla unknowns? The fact that we don't know something, or don't bother to ask questions in an attempt to understand things better, does that constitute anything more than laziness on our part? A symptom of an underlying complacency rather than a confrontation with an unfathomable mystery?
I found myself still puzzled by the unknown unknowns. Finally, I came up with an explanation. Using the expressions "known unknowns" and "unknown unknowns" is just a fancy — even pretentious — way of talking about questions and answers. A "known unknown" is a known question with an unknown answer. I can ask the question: what is the melting point of beryllium? I may not know the answer, but I can look it up. I can do some research. It may even be a question which no one knows the answer to. With an "unknown unknown," I don't even know what questions to ask, let alone how to answer those questions.
It's all about how the incompetent can't know they are incompetent.