Suppose you have several notebooks full of potential story and character ideas, but those ideas are fragmentary. Most of your ideas are undeveloped and take the form of, "I wanna write a historical novel about person_X," and "It would be really cool if one of my characters had personality_tick_Y," and "Wouldn't it be beautifully tragic and ironic if event_Z happened."
Suppose while reading Wikipedia about certain persons of alleged history, you decide definitively that you've found the character you want to write about, period. This person may never have existed and is considered by most scholars to be fictitious. You're already jotting down notes and outlining the progression of the plot.
After a while, you stop writing to finish reading the Wikipedia entry, and you discover, to your overwhelming frustrating, that someone else has recently (within the last eleven years) written a work of historical fiction about the same character. Your plot lines and character traits are fairly different and the other author's book has been both adored and disdained by readers. The biggest threat is that there might be a motion picture planned in the next two years, but until now, you've never heard about it.
What do you do? Do you write your story or do you set your notes aside and pick another historical person? Do you continue with your own version of the story and hope that a publishing company would print and distribute your novel despite the competition from this already established publication? Or do you admit the inevitability of your defeat and move on, trusting that you'll find inspiration again?