This is a common phrase bandied about by authors, at least in part to protect themselves from the people around them shoving ideas at them and asking them to share profits on the published manuscript which the author now writes. It's also a way of defusing the tension over the oft-asked question "Where do ideas come from?" The truth is that authors don't know where ideas come from. Or, at least, they don't know why some ideas matter to them enough to write a book about them and others don't at all.

I think ideas matter a lot. There are some books that just don't have any ideas in them. Or if they do, they are so hidden under cliche that they don't matter. I get bored with these books.

On the other hand, I've read entire books that were not written in what seemed to me the best style, simply because the idea was so captivating. I had to find out what happened. The whole plot of a book or even a series can be based on a single idea brought to conclusion. I wonder sometimes if the idea popped into the author's head full-grown or if he wrote ten different drafts before he crystalized it into the perfect idea. But once that idea is set, the whole book revolves around it. It almost writes itself.

Of course, my favorite books have an incredible idea and then twine characters around that idea until the two are inextricable, there is great plotting, a great new world and magic (or science) set up around it.

So, ideas matter. The best ideas are incredibly valuable. But they can be improved on. And even the perfect idea still has to be made into a book, by someone who knows how to do it. A perfect idea, however, is actually pretty hard to find.