When someone tells you a joke, they are expecting a laugh from you. And it feels odd if you don’t understand the joke and no response comes from your side.
The person who is telling the joke has to explain it, and the situation no longer remains humorous.
Similar case with user interface.
When a user comes to your product, they should be able to find the possible actions they can perform with the design.
If a user interface has to explain itself to its user at each step, it is not possible to navigate the user flow smoothly.
A self-explanatory design guides the user while he is working on it. It provides necessary help and guidance to its user in a natural way. No one wants to refer to help manuals each time they get stuck into something. Instead, the user leaves the product when they are not able to achieve their goals efficiently.
A good design helps its users graciously by providing necessary information, warning and error messages as per current situation.
A design should be self-explanatory and understandable for the user by making ease of use its priority. Ease of use is the top most important feature frustrates users when missing.
“If you find an element of your interface requires instructions, then you need to redesign it.” — Dan Rubin
The best way to create an understandable design is to get frequent user feedback and enhance the user experience based on it.