In the old days, we thought of errors as unavoidable, and so we defined high quality as “conformance to specification” and low quality as “outside specification.” (More on this in my article on the Taguchi Loss Function.) This was the era of quality control, where we tried to control quality by inspecting out what was nonconforming and hoping that what we were sending was conforming. Because inspection is less than perfect (some sources say human inspection is about 80 percent effective) then if there were a nonconformance, it had a certain probability of getting through inspection and to the customer. Although we tried to control the quality of the output, we weren’t always successful. But that was OK, because our customers didn’t expect everything to meet specifications anyway, just as we didn’t expect everything supplied to us to meet specifications.