Dr Taguchi was best known for his work on the loss function approach to quality evaluation – maintaining that it was no longer good enough to consider quality merely in terms of conformance to specification. He argued that loss of performance occurs progressively with incremental departures from the nominal, thus presenting a powerful call for the continuous improvement of process rather than reliance on a pass-fail system based on specification tolerances. In other words, whenever there are variations from nominal (as there always are), then some loss is being incurred, so the need for improvement (reduction in variation) is ever present.
Taguchi developed the use of statistically based experimental design to ensure robustness of both product and process design. It is necessary only to look at the record of reliability in service of Japanese vehicles, cameras, consumer electronics, machine tools etc. to see the proof of the pudding.