I've got a million of 'em. News stories, friends' anecdotes, observed oddities, all form possible stories in my head. The next step is to try to write them down, and here I'm successful about a third of the time. It's heartening to know that big authors struggle with the same problem: Michener did all the notes for IBERIA decades before he actually wrote the book, and authors like Martha Grimes express frustration that they have other ideas they'd like to work on while their agent/editor/public demands more of The Same.
So I'm betting we all have novels begun that either fizzled or got pushed aside due to other priorities. They sit there, and in my case, I take a look from time to time and think, "This isn't bad. I should finish it." I may even write a chapter or two. But maybe it isn't coming together, it isn't what I know is selling, or it just needs more work than I can give it at the moment, so it goes back to its file and waits.
Give up on it? I probably never will. Finish it? Maybe not that either. In fiction as in life, not all stories have an ending. We're not willing to give up on them, but we just don't know where they need to go.