At a February 12, 2002, news briefing, Secretary of Defense Donald Rumsfeld explained the limitations of intelligence reports: "There are known knowns. There are things we know we know. We also know there are known unknowns. That is to say, we know there are some things we do not know. But there are also unknown unknowns, the ones we don't know we don't know."

A known unknown is information whose existence someone is aware of but does not possess. Known unknowns are what drives many scientific experiments, search engine and database queries, business intelligence (BI) and data analytics, among other channels of inquiry.

 "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. "

This saying is typically used to conduct risk management analysis by splitting the upcoming obstacles into 3 categories:

Known knowns — things that we know (i.e are aware of) that we know. These pose less of a risk, as they are facts we are confident in.

Known unknowns — things that we know (i.e. are aware of) that we don’t know — they imply a risk, but since we know them we can measure the risk, understand it and investigate more to make this a known known.

Unknown unknown — things we don’t know (i.e are not aware of) that we don’t know. These are probably the most dangerous since these encompass what we are not aware of and therefore can’t plan, analyze or take actions to mitigate them. You’ll have to do some thorough exploration to find the things you don’t know that don’t know.

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