Again and again, I have started a book with an inkling of an idea and an image only to make it fifty pages and decide to start over. I may have developed the perfect setting, the perfect characters, and the perfect plot. Though, there is something about the story being written which mirrors what readers would expect. When writing this way, the writing can appear to be...well, writing.
Writers must be willing to write in the same way that they live to fulfill their dreams. Be satisfied with uncertainty, ambiguity, and mystery. Good ideas have already been written. You have to be willing to change the way you think about the world - to take the road less traveled - and kill your good ideas for better ideas.
Spend some time daydreaming, or reading another book, or exploring the world around you. Look at life through a different lense than the norm, and be okay with telling the story therein. When you are knee-deep in your story and something better comes along, be comfortable with rewriting the story. Sometimes the change is well worth the effort.