From the physics principal of inertia we know that the velocity (direction and speed) of an object cannot change instantly.  Any change, however quick, happens over a period of time.  This means that there is a relationship between what has gone before and what is to follow.  The larger the forces applied to an object the weaker this relationship but this relationship always remains.

Also, our brains which, control our actions, are subject to emotional states that themselves take time to change.  This fact combined with inertia forms the following:

Principal of Continuity: The state of the system at any one instance influences future states and is influenced by previous states.

We will use this principal to help form theories to test against and interpret real life data.  For example, we may analyse the relationship between impacts and follow throughs, the presence of returns and unwanted tension, or changes of direction in court movement.