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C00036554 (19)), "actors tend to perceive what they expect," then these expectations furnish greater leverage to a deception plan — a form of mental jujitsu. Such a maxim, termed Magruder's Principle5 by Lewin, appears to be well appreciated by deception planners, and is consistent with numerous studies on the psychology of perception. David Mure (23), for example, recalled that one of Brigadier Dudley Clarke's inflexible rules for development of cover plans was that "all cover plans should be based on what the enemy himself not only believes but hopes for." Clarke was one of the leading deception architects for the British in North Africa and the Middle East and, according to some, the best deception planner in WWII (63).

There is ample historical evidence to confirm the efficacy of Magruder's Principle. Figure 1 contains entries from the historical data base described previously. These entries (including both strategic and tactical cases) are categorized according to whether or not deception was employed, whether or not plans were keyed to enemy preconceptions and whether or not surprise was achieved. Analyses of these data, shown also on Figure 1, enable two conclusions to be drawn. First, historically, deception schemes have more often