The Zeroth Law of Unreliability

Oct 14th, 2002 by Tony in QSM2

“If a quality, like reliability, is not clearly specified, you can deliver the project earlier, if you interpret the quality requirements as “whatever it happens to be when the deadline arrives.” This, coupled with an innocent “Oh! You wanted more than two minutes between failures!” after the first complaints arrive, will solve the deadline problem initially. You are of course prepared to discuss a new schedule and project for enhancing quality to the required levels, not clarified for the first time”

— Tom Gilb

I like to quote Tom Gilb’s observations about what he calls “Weinberg’s Zeroth Law of Unreliability.” It represents the only time I can remember winning an argument with Tom. After he had published his “Gilb’s Laws of Unreliability”, I commented that he had left out the most important one of all, the Zeroth Law:

If a system doesn’t have to be reliable, it can meet any other objective

He argued that nobody could be so stupid as to not know that law, but a year later he admitted that most of his clients didn’t seem to know it at all. Moreover, they were desperately trying to remain ignorant of the law, and to keep their customers ignorant so they could use the escape hatch that Tom describes in the quotation above.

— Jerry Weinberg, Quality Software Management Vol 2, Chapter 19

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