In his book The Design of Everyday Things, Don Norman explains different concepts that help improve designs. The focus of the book is mostly functional. One of these concepts is constraints.

Constraints make it easier to use an object as it was intended, by making it impossible to do anything else with it. For example, we can think of a car door handle where you have to put your hand in and pull the latch out… it is impossible to do anything else with this form of handle. You can’t push it, you may only pull it. But constraints may also be given by different cues, which can be physical like the door handle, visual, or cultural.

This lego motorcycle is composed of 18 parts, most of which are unique, but others which are similar in size and shape but differ in color. An example of a cultural constraint would be the placement of the three colored blocks representing lights: the blue police siren lights, red brake lights and yellow headlights. They are all the same shape, but the colors allow the user to infer their placement.

Using cultural constraints, even a young person can achieve the intended final result, thanks to effective design.