So, suppose you come up with a story setting. It has several elements that you think mesh together really well, you have character traits that you think could produce some interesting situations, and overall you think that you can make some well-thought out stories in this setting. 

Now suppose you come across a long-running book series that you have never read, or even really knew existed, but whose setting is nearly identical to what you came up with. And by identical I mean many people would think that you had simply copied this other author. 

Would you still use what you came up with, or would you scrap it entirely?