Alone we can do so little. Together we can do so much.
-- Helen Keller
There are many different elements involved in creating a successful product. From research and visual design, to development, copy, information architecture, marketing, and SEO, the list goes on. Even with the best intentions, a design is only one of the parts.
All parts involved have to have equal weighting.
If a product is hard to use, despite even the best design, the product will not be successful.