You know a lie is being told when you hear some (unsubstantiated) numbers.
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The project will be done in 1 year or 6 months or 1 week. 

These are numbers people just make up because they don't know the real numbers. Often there is no choice but to use such numbers, but when you hear them, understand that they represent uncertainty and risk.

''Dates are often the most realistic numbers provided, as there is often an underlying reason for the date.  It is usually "done" that is the variable and one must be willing to define (and redefine) done to meet the date.''
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"Nothing is true.  Everything is permitted." -- Hassan i Sabbah
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17 is the least random number. Really. Try it.

''Do you mean:''
	* ''Of all random numbers, 17 is the smallest.''
''or''
	* ''Of all numbers, 17 is the most un-random.''
Numbers are not random; sequences can only approximate randomness; randomness is only a concept.

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Of all fractions, phi (or tau) is the least random: (sqrt(5)+1)/2. Next time you drop a frame onto the screen, instead of centering it vertically, move it up towards the top by this ratio:

 frame.setTop((screen.height-frame.height) * 381 / 1000);

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10%. This number crops up everywhere and never seems to have any supporting data.  10% increases in performance.  Estimates made within 10%.

Another one:
 "I am a one in ten
  A number on a list
  I am a one in ten
  Even though I don`t exist
  Nobody Knows me
  Even though I`m always there
  A statistic, a reminder
  Of a world that doesn't care"
(UB40's "One in ten")

Edit: One In Ten by UB40 refers to the unemployment rate in Britain in the late 80's, but plays on the idea of people as statistics, thus the use of the most commonly referred to percentage by the media.