In physical warfare, the inherent instability of every situation is concealed by the apparent definiteness of the operation. Panic, revolt or dissolution of regiments is not normally figured into the situation. The assumption is made--and for professional military purposes must be made--that all identical units are of equal quality unless proved otherwise, that all men in a unit will respond with psychological uniformity unless they are reported out physically by medical reports, that the unit will be capable of doing tomorrow what it did yesterday. The terrain comes in as a constant factor and even such variables as weather can be calculated in terms of a predictable risk. Nevertheless, every experienced soldier knows that things do not always work out the way they should, that unexplained or unforeseen factors sooner or later complicate or frustrate the best plans, and that warfare is a huge gamble with a superficial but very necessary coating of exactitude. In psychological warfare, these considerations apply even more sharply. Combat at least has terrain, order of battle, logistics, estimated capabilities and other concrete factors with which to figure. There is a known degree of difference between one enemy division and five enemy divisions. There is the possibility of computing the time which the enemy will need to fulfill this capability or that, and the equally good possibility of computing time on our side for countermeasures. Even in such very long-range operations as strategic bombing, economic factors can be figured out to give the operation at least the coloration of precision. With propaganda, none of this is possible. The propagandist never knows the terrain, because his terrain is the enemy mind in its entirety--a factor beyond the understanding of any man. The enemy can have strongholds of faith to be shaken but the propagandist can never say, "This factor is finished. Therefore we proceed to the next." There is neither victory nor defeat, only the endless seesaw of probable accomplishments or probable blunders. The honest psychological warfare operative will admit that he does not know where he is at any given moment, how far from his start, how near to his goal. Even with surrender of the enemy, propaganda cannot be judged to have met with complete failure or complete success, because propaganda is an interminable stream going on into international affairs and carrying over to the next war. Psychological warfare can be given apparent certainty only by the creation of assumptions on the part of the planner. The assumptions will not stand up if questioned by a clever philosopher, any more than did the basic assumptions of the German General Staff when questioned by the sardonic Trotzky at Brest-Litovsk. Nevertheless, the assumptions can work for planning purposes.