The concept of the British Army’s ‘learning curve’, stemming from the work of Peter Simkins and other 'revisionist' historians, became popular yet fell under the shadow of criticism for being simplistic. It was, of course, at best a shorthand description of the operational and tactical progress of the BEF. There was (as the originators of the concept fully understood) never a smooth ascending curve of increasing competence – there was, rather, a rollercoaster of ups and downs. This, as William Philpott has pointed out, was the result of a ‘dynamic process of adjustment to new technologies, more sophisticated and flexible tactics, novel operational doctrines, complex logistics and fundamental change in the systems of command, control, communications and intelligence’.  Further, one need look no further than the writings of Carl von Clausewitz  to understand why such a progress could not be smooth. Clausewitzian concepts such as uncertainty (‘the fog of war’), friction, and the independent will of the enemy always indicated why this could never be so. As Clausewitz stated: ‘Friction is the force that makes the apparently easy so difficult.’  The concept ‘encompasses uncertainties, errors, accidents, technical difficulties, and the unforeseen, and their effects on one’s decisions, actions, and morale’.  Further, war is an activity in which one side’s will is pitted against the independent will of the other. Thus, the Germans underwent their own learning process. Each step in either side’s development brought forth from their opponent a reaction and counter-development.