Georgy Saveliev
The six dimensional usability model

It is nearly impossible now to identify a true origin of the statement: “Nothing is more practical than a good theory” repeatedly cited at different times by prominent scientists of various nations. If we substitute in this phrase “theory” with “model”, it will probably make more sense for those of us who prefer another citation: “The difference between “theory” and “practice” is that in theory there is no difference between theory and practice, but in practice, there is…”