The rationale for studying fatigue and fatigue mechanism is examined by considering two fundamental problems in engineering, namely, the problem of feasibility, by asking whether a product works, and the problem of fatigue, by asking whether a product lasts. It is shown that the first problem (feasibility) is easier than the second (fatigue) because the solution to the second requires experimental information of a time scale incompatible with that available to the engineer or the material scientist. To resolve this dilemma, it is proposed that advances in computer-aided quantitative microscopy, fracture mechanics, and many other allied disciplines, be incorporated in measuring microstructural changes due to fatigue at a time scale workable in a laboratory. It is concluded that such study in discovering fundamental mechanisms of fatigue holds the key to the solution of the second fundamental problem in engineering.