Remember that graphic design, in all its forms; logos and identity, brochures, websites, user interface and experience, road signage, birthday cards etc., is all essentially communications.
When a client asks a designer to design something for their business it's imperative that the designer knows as much about that project as possible and as a designer, it's your job to gain that information. Without knowledge of the product / service, the message that is to be communicated and to whom that message is for, the designer simply cannot 'design'.
For example, a green button on a website isn't green because it was the designer's favourite colour that day, it will be green to encourage a user to take a positive step and click on that button. A brochure will have clear typography with hierarchy; main headers, sub-headers, lead-in copy, body copy, footer captions etc., which all lead the reader's eyes through the content in a purposeful manor. It's all very intentional.