To go a bit deeper conceptually:
“Anyhow, the older I get, the less impressed I become with originality. These days, I’m far more moved by authenticity. Attempts at originality can often feel forced and precious, but authenticity has a quiet resonance that never fails to stir me.”
― Elizabeth Gilbert, Big Magic: Creative Living Beyond Fear
(I love this book and highly recommend it.)
While directly ripping someone off is wrong, I think truly original ideas don't happen often. I think most people have had ideas similar to pre-existing work, it's just a matter of making it yours. My comic, Pretty Power Princess, is one of several comics about a captured princess that escapes. It's not terribly original in and of itself. However, I have woven in differences that make it stand out. (Or at least I try to.)
Archetypes exist for a reason. Don't give up on a good idea because someone did something similar. Especially if you're really hyped up on the idea. Just see how you can push it or twist it to make it yours. Sometimes the best of themes/stories/concepts take a path that was unexplored in a well-worn genre. Harry Potter wasn't the first book about wizards or even the first book about young wizards. It just found it's own path.
Again, not supporting outright plagiarism. But too many people waste time waiting for a truly original idea. I just think this is worth discussing.