Traditional Principles of Animation/Anticipation
Anticipation is a preliminary action that sets up a primary action. It cues or prepares the audience for what is about to happen. Let's look at an example. Let's say that a steel cable is being stretched extremely tight by two opposing forces. Before the cable snaps in two, you position your camera for a close up on the actual breaking point. The close up shows the cable fraying as more and more tension is applied. Seeing this, the audience automatically anticipates what's about to happen (the eventual breaking of the cable).
In some cases anticipation is needed physically. For example, before you can throw a ball, you must first swing your arm backwards. As the arm goes back, the audience anticipates it coming forward and releasing the ball. more important than just audience anticipation... there is a need for a set up to the coming movement. every movement requires anticipation and recovery. there is a need to show a transfer of weight before performing an action. it is here where the action is set up.
Anticipation is also required to simulate real motion. If an object is at rest, some preliminary action that transfers energy to the object must occur so that it can use that energy to execute the primary action. Before a character can jump, they must crouch down and swing their arms for counter-balance. By seeing the crouch, the audience anticipates that the character is about to jump.