Familiar patterns let people begin with knowledge instead of instructions.
Someone wants to review a purchase, so they look for a cart near the top of the page. If it sits behind an unfamiliar symbol in the footer, the interface has turned a routine action into a search problem.
Origin
Jakob Nielsen articulated the principle in his work on web usability. People form expectations across many products, so a new interface inherits conventions it did not create.
Study the products your audience already uses. Look for conventions they rely on, not only visual trends your competitors happen to share.
Keep common actions predictable. Navigation, search, saving, closing, and going back rarely benefit from a new interaction language.
Break convention when the familiar pattern causes a real problem. Make the benefit clear enough to justify the learning cost.
When a new pattern is necessary, teach it in the moment and keep it consistent. One clear lesson is better than repeated surprises.
Digital systems
A familiar shopping cart
The cart uses a recognizable label and stays in a conventional part of the header. People can transfer what they learned elsewhere and continue without instruction.
Physical signals
A light switch by the door
People reach near the entrance because that is where switches are usually placed. A switch on the far wall may work perfectly and still feel wrong.
The product changes a familiar pattern without enough benefit, so people pause, search, and doubt knowledge that normally transfers between systems.
Follow established patterns for common work, then introduce new behavior only where it solves a problem the familiar pattern cannot.