Magruder's Principle: Named for Confederate general John B. Magruder, this principle states that it usually easier to deceive a deception target into holding on to a pre-existing belief than it is to convince the target that something the target believes to be true is not. Examples include the Allies of World War II making use in the Operation Mincemeat deception of the pre-existing German belief that Greece and the Balkans would be their next invasion target after North Africa, when the Allies actually intended to invade Sicily.