You've just started your new book, and you're excited. Everything is great...until you go to the movies, and you see a trailer for a plot that looks exactly the same as your new book. Being an author means you have to know when to change your story.
Simpsons Did It
I had to face a similar circumstance recently. I went back to an old project to complete it, and found that one of my characters has the same name as a character in another book series. A much more popular book series. And it's also a TV show. And even if I were to take a magic potion, my book isn't going to become as popular as that other book. Doesn't that mean that I have to change my story?