Law of Continuity
Connecting elements to a continuous flow
Users know how lines flow by nature. Interfaces look more appealing when they have a flowing line instead of multiple separated objects that feel like they have no connection to each other.
A good example of the law of continuity is probably to use grids in visual designs because then all UI elements are ordered and those that follow the same line will be connected to each other by the users automatically.
Visual design plays an essential role for the user experience of a product, software or service.