Things that cannot possibly go wrong

From:         Pete Mellor <>
Date:         05 Jan 93 00:24:11 PST
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The following extract from Douglas Adams' latest book* contain a lesson 
for designers of complex systems, particularly computerised ones (e.g., 

     ... all mechanical or electrical or quantum-mechanical or hydraulic or 
     even wind, steam or piston-driven devices, are now required to 
     have a certain legend emblazoned on them somewhere. It doesn't matter 
     how small the object is, the designers of the object have got to find 
     a way of squeezing the legend in somewhere, because it is their attention 
     which is being drawn to it rather than necessarily that of the user's. 

     The legend is this: 

     `The major difference between a thing that might go wrong and a thing 
      that cannot possibly go wrong is that when a thing that cannot possibly 
      go wrong goes wrong it usually turns out to be impossible to get at or 

* "Mostly Harmless" (The fifth book in the increasingly inaccurately named 
  "Hitch Hiker's Guide to the Galaxy" trilogy) by Douglas Adams, Heinemann, 
  London, 1992, ISBN 0434 00926 1 

Peter Mellor, Centre for Software Reliability, City University, Northampton 
Sq., London EC1V 0HB, Tel: +44(0)71-477-8422, JANET: