As a graphic and brand designer this is my #1 rule I live by.
What does it mean? It means that we should always work on figuring what the function needs to be, and the best ways to make that function work.
One of the best examples of a beautiful function first design is the spoon. The spoon has a sensual sort of shape to it. No one set out to make it that way, all of the curves and parts are designed to do one thing. Bring liquid from a bowl on a table to your mouth without spilling.
This is no small feat. It is a miracle of geometry and physics that was produced over hundreds of years by many different designers.
The point is, the spoon is a perfect example of a function first design, it looks great because it works so well with the human body.
In a similar way, when designing branding and graphics, if the need is considered most important and the function of communication is considered first, then the graphic or brand is far more likely to work.
In other words the question “What is it for?” Is far more important than, “what does it look like?” Focus on what it’s for with reckless abandon and in the end it will look great.