Men at work turn out a net product because they know how and are interested in doing it; and their output is limited by the industrial methods which they have the use of. But the output is limited in such a way that it always exceeds the cost by more or less, barring accident. By and large, throughout past time the industrial arts have been gaining in efficiency, and the ordinary margin of net product over cost has consequently gone on widening. This is much of the meaning of "an advance in the industrial arts."

The Vested Interests and the Common Man (1919)