I asked myself something yesterday when I was trying to decide which of the many possible story ideas I should commit to working on next. I'll share it with you in case you have some decision to make, to which this line of questioning may apply.
I essentially had three story ideas revolving in my mind as main contenders for The Next Novel; we'll call them A, B, and C. (As with many writers, my problem isn't coming up with ideas, it's choosing which of my many ideas to use at a given time.) Naturally I first tried asking myself, "Which do I want to write most?", but for some reason that didn't give me a clear winner. I could justify why I might like writing each of them, or "should" try writing each of them.
So I turned it around and instead asked, "How would I feel if I learned that someone else just wrote and published this exact story, and therefore I could never write it myself?"
And that was more interesting. Because for stories A and B, it turned out I didn't mind so much. I thought, "Oh well; that might be for the best. Someone else with more expertise on subject A or subject B would probably write it better." But for story C, I felt regret at the idea of giving it up—"Aw! I could've had fun with that. I would have come up with something cool."
Thus we have our answer.
...Although don't hold me to that. I could yet change my mind.