1. Garbage In, Garbage Out. A reference to the fact that computers, unlike humans, will unquestioningly process the most nonsensical of input data and produce nonsensical output. Of course a properly written program will reject input data that is obviously erroneous but such checking is not always easy to specify and is tedious to write.
GIGO is usually said in response to users who complain that a program did not "do the right thing" when given imperfect input or otherwise mistreated in some way. Also commonly used to describe failures in human decision making due to faulty, incomplete, or imprecise data.
For example, a badly written TeX document will look bad because the user did not correctly typeset the TeX source properly. This instance of GIGO could be described in a similar vein to WYSIWYG - what you see is what you get.
2. Garbage In, Gospel Out. This more recent expansion is a sardonic comment on the human tendency to accept the results from
computer systems with unquestioning faith. A person who suffers from GIGO
believes in heaven while behaving like a sucker.
An example of this blind-faith GIGO mentality is to believe that
your work, stored in a computer, will be there whenever you need it
even though you never perform data backup or virus scan.
See also
References