Until the publication of my first novel, I'd never consciously thought about the importance of cover design. But the graphic artist's crucial role in the novel's production (and possible success) became apparent. The artist's talent was vitally important to the commercial viability of the novel.
The one thing that's consistently true about all bestselling authors is that they are on a mission, driven to share their wisdom. While fame and fortune may come their way, that isn't the reason they write.