Unknown Unknowns

Consider the following opening paragraph of an old version of the entry unknown unknowns in Wikipedia (April 15, 2010 version):

In epistemology and decision theory, the term unknown unknown refers to circumstances or outcomes that were not conceived of by an observer at a given point in time. The meaning of the term becomes more clear when it is contrasted with the known unknown, which refers to circumstances or outcomes that are known to be possible, but it is unknown whether or not they will be realized. The term is used in project planning and decision analysis to explain that any model of the future can only be informed by information that is currently available to the observer and, as such, faces substantial limitations and unknown risk.

The concept gained global exposure on February 12, 2002 when Donald Rumsfeld, the then United States Secretary of Defense, explained that:

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.

Another take on this concept is given by Hillson (2007, p. 22) who builds on a saying attributed to Confucius “… To know that we know what we know and that we do not know what we do not know — that is true knowledge …” . Hillson elucidates the concept through four combinations of (Knowledge, awareness) pairs. The state of ignorance represents unknowns unknowns and is characterized by the absence of both knowledge and awareness.

The difficulty presented by Unknown Unknowns is not that they prove hard to quantify, nor for that matter, that they defy a qualitative analysis. The point about Unknown Unknowns is that they are “unknowable”. We simply wouldn’t know what to describe much less what to quantify. For this reason Hillson (2007, p. 22) concludes that ” … Unknown-Unknowns are nothing to do with risk management …”.

On a more positive note, as shown in the book, voodoo decision theories have no problem at all coping with Unknown Unknowns! They can basically cope with anything. Their use is only limited by … our imagination!

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