Now, it is known to psychologists that certain sensations attract favorable attention in a larger number of cases than others. For example, in an appeal to the eye, rectangular shape in proportion of three to five, that is to say, three units of measurement wide by five units of measurement long is more likely to attract favorable attention than a square. Similarly, any object in motion or having the illusion of motion, is more likely to attract favorable attention than an object at rest. Black letters upon a white background attract more favorable attention than white letters upon a black background. Many such psychological problems have been worked out. They are valuable, but they have no place in this work, since our task here is not to deal with averages, but rather with variations in individuals—how to discern them and how to deal with them.
In a similar way, psychologists have determined that the average individual more quickly becomes interested in that which he can understand than in that which he cannot understand, in that which appeals to something in his own experience than in that which has no such appeal, in that which appeals to his tastes and his feelings than in that which appeals to his judgment. These are rules applicable to the average, but they are very general and are of little use to you unless you add to them specific knowledge of every individual whom you wish to persuade.
Desire, as you will see by the terms of the law of sale, is merely interest intensified. Desire is the main spring of action. It is the real force of every motive. Contradictory as it may seem at first sight, people always do what they want to do even when they act most reluctantly. Their action is inspired by a desire to escape what they believe to be the certain penalty of inaction or of contrary action. The boy who slowly approaches his father to receive a promised whipping, does so because he wants to. And he wants to because he knows he will be whipped so much harder if he runs away. Desire is, therefore, the great citadel toward which all of the campaign of the persuader must be directed. Given a powerful enough desire, decision and action follow as a matter of course.
Psychologists have determined that imagination is the most powerful mental stimulus to desire. Imagination presents to the mind, as it were, a more or less vivid mental picture of the individual enjoying the gratification of his desire—be it physical, intellectual, or spiritual. The longer this picture remains in the mind, the more vivid it becomes, the more it crowds all other thoughts and feelings from the mind, the more powerful and irresistible becomes the desire. It is the task of the persuader, therefore, to stimulate the imagination to the painting of such mental pictures. This we well know, but