Whose story is it, anyway?

She was doing fine, writing her NaNovel, when an unplanned character appeared on her page and stole her heart, outdazzling her main character and taking over the stage.

Is this a wonderful gift from the muse, or just a case of that shiny object flitting across her screen and derailing a perfectly good tale?

That depends on how the writer handles the situation.

Has this happened to you?  How did you handle it?  How did it work out?  Share your experiences and views.