"The Gestalt LAW OF COMMON FATE states that humans perceive visual elements that move in the same speed and/or direction as parts of a single stimulus. A common example of this is a flock of birds. When several birds fly in the same direction, we normally assume that they belong to a single group. Birds that fly in a different direction do not appear to be included in the said group. A marching band is another example that usually exhibits the gestalt law of common fate. Below is yet another example showing this principle [as the bubbles are grouped together in their movement off the page]."
Common Fate is often confused with Gestalt's Principle of Continuity. Common Fate is more about suggested movement while Continuity is about resting objects that are not continuing dynamic movement.
"The principle of good continuity holds that humans tend to perceive each of two or more objects as different, singular, and uninterrupted object even when they intersect. In other words, individuals tend to group together as well as organize curves, lines and other forms that are found in similar directions. However, those that establish changes in direction may be perceived as different objects. The alignment of the objects or forms plays a major role for this principle to take effect. This principle is well used by educators in teaching young kids on how to write the letters of the alphabet as well as draw images. Below is an example showing the Gestalt law of good continuity [as you follow and connect the lines in the pattern though they don't actually connect."
Below is the iconic album cover for The Beatles Abbey Road. This shows both Common Fate and Continuity. The 4 band members walking the same direction shows Common Fate. (Consider what would happen if one were walking the other way. This would be using the Law of Common Fate via violation of it.) The law of Continuity is used on the smaller broken white lines in the middle of the street (not the crosswalk). We continue those as one line. It is easy to confuse the Law of Common Fate and Continuity. But in this case, the 4 band members are only Law of Common Fate while the lines in the street could be argued to show both.