The fifty percent rule
What is the [jazz] soloist doing when he attempts to “build?” Actually the ideal process hardly ever takes place—that is, it is hardly ever the case that a conscientious soloist plays a thinking solo for a hard-listening hearer—but when this does happen, the key process is memory. The soloist has to establish for the listener what the important point, the motif if you like, is, and then show as much as he can of what it is that he sees in that motif, extending the relationships of it to the basic while never giving the feeling that he has forgotten it. In other words, I believe that it should be a basic principle to use repetition, rather than variety—but not too much. The listener is constantly making predictions; actual infinitesimal predictions as to whether the next event will be a repetition of something, or something different. The player is constantly either confirming or denying these predictions in the listener’s mind. As nearly as we can tell…the listener must come out right about fifty percent of the time—if he is too successful in predicting, he will be bored; if he is too unsuccessful, he will give up and call the music “disorganized.”
Thus if the player starts a repetitive pattern, the listener’s attention drops away as soon as he has successfully predicted that it is going to continue. Then, if the thing keeps going, the attention curve comes back up, and the listener becomes interested in just how long the pattern is going to continue. Similarly, if the player never repeats anything, no matter how tremendous an imagination he has, the listener will decide that the game is not worth playing, that he is not going to be able to make any predictions right, and also stops listening. Too much difference is sameness: boring. Too much sameness is boring—but also different once in a while.