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"There are unknown unknowns" is a phrase from a response United States Secretary of Defense Donald Rumsfeld gave to a question at a U.S. Department of Defense (DoD) news briefing on February 12, 2002, about the lack of evidence linking the government of Iraq with the supply of weapons of mass destruction to terrorist groups. Rumsfeld stated:

Reports that say that something hasn't happened are always interesting to me, because as we know, 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. And if one looks throughout the history of our country and other free countries, it is the latter category that tends to be the difficult ones.
The statement became the subject of much commentary. In The Decision Book, author Mikael Krogerus refers to it as the "Rumsfeld matrix". The statement also features in a 2013 documentary film, The Unknown Known, directed by Errol Morris.Known unknowns refers to "risks you are aware of, such as canceled flights," whereas unknown unknowns are risks that come from situations that are so unexpected that they would not be considered.

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  1. C

    Unknown lead (?) Pipework to building exterior

    Hello all, I'm preparing an estimate for a bathroom renovation in a block of flats. As always I'm trying to flag up / plan for and cost as many possible unknowns as possible in advance. One thing that I've not seen before is the ~50mm pipework connecting into the soil stack (see picture). My...
  2. J

    unknown pipe in old fire-place.

    All, Belfast, Northern Ireland. I am in a bit of a predicament. I have recently had a stove fitted in a chimney that had a disconnected and capped gas fire. The old gas line went straight out the back wall and was visibly capped a short distance from the gas meter. A simple pull out job. Upon...
  3. T

    Unknown pipe after pump

    Hello does anyone know what this pipe is which diverges from the main pipe after the central heating pump. It seems to connect to the return pipe from the cylinder, so I guess it isn't a bypass?
  4. R

    Any ideas on what this part is??

    Had a plumber in whilst I was on holiday to fix a leaking condensate pipe on system boiler but have noticed he’s also fitted something on my unvented cylinder on the return secondary circuit. I’ve circled the part on the two pics. Anybody got any idea of what this is? Plumber not returning any...
  5. L

    unknown shower makes

    hi has anyone got any idea who makes this shower and where i can get parts?
  6. T

    Sink leaking; unknown part name causing the issue

    Please see the attached photo - the part causing the issue is circled in red. We have taken apart the sink and cleaned out all the pipes as we thought that was causing the issue. But the issue remains. When the sink is draining the water floods up around the two small flexible pipes you can see...
    • t_frank
    • Thread
    • america causing issue leaking parts sink unknown usa
    • Replies: 3
    • Forum: USA
  7. U

    Unknown substance in sink drain

    My sink emits a whiff of something when hot water is used. It isn't the water itself. I've used bleach-based drain cleaners and soda and vinegar to no effect. I took a good look down the drain and found the attached. Whoa. It isn't scoopable. It feels more like soft rubber and is a single...
    • Ulysses
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    • america drain sink unknown usa
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