I'm not one who considers any thrown out material wasted. For one it acts as a teaching tool, showing me what does and does not work, and sometimes discarded ideas become part of another story. Case in point with today's blog post. It tells of a story I wrote years ago that eventually got scrapped because it just plain sucked. However, one of the ships, and a handful of secondary characters from the story found their way in as the main characters in another saga I created. So yes, the original story failed, and was ultimate scrapped because of this, but in the end elements of it survived and became the foundation for another story that not only succeeded, but also spawned a whole series of other books, each of which was progressively more successful.
So in the end, I don't see these as ultimate failures. Merely explorations and learning experiences, some of which get used, and some of which get scrapped. But in the end they all become useful in some way or another.