Law Of Common Fate
The law of common fate is a principle of perception in Gestalt psychology and is the tendency for people to perceive items moving in the same direction as being more closely related than objects that are moving in different directions or are immobile.
Here's a way to picture the law of common fate - imagine you are driving down a busy highway with many other cars. When heading in the same direction the vehicles have the perception of being related to one another and a common moving mass. When something is contrasted or against the law of common fate (such as a car headed the wrong way, one weaving and swerving erratically, or an immobile broken down car) we immediately perceive this dissonance as it seems out of place.