This is only 10 pages. Written by an air force colonel - PhD -
  on the dangers of metaphors.

  That's where we take the logic from one sphere of knowledge and
  apply it to another sphere of knowledge to generate a conclusion
  in the minds of the audience.

  it's used for good, but it is also misused. and if you don't
  feel like reading it, this graphic I snipped form it sums up on
  the problem.. *especially* of "what if* stuff but of
  metaphors/analogies in general.