After enjoying the ride of an exquisite story, I'm often inspired and juiced up to create one; other times, I'm totally depressed (the Harry Potter series manages to breed both effects in me).
I start to worry... I'll never do this as well as he or she did. I can't even... Or, oh shit! That's my idea about a dead protagonist--someone got to it first! I thought it was unique! Now here it is, played out in a dozen different books and movies. (My guy's not a vampire, so at least he's got that going for his uniqueness...)
Soon follows the nasty realization that every artist has contended with: it's all been done before. It's all been done stunningly, unbelievably well. And it's been done badly. However you slice it, someone has already diced it.
It's true. Just breathe with that...
And don't you dare give up on your projects because of it.
I can't imagine many chord progressions, metaphors, plot twists, color schemes, or jokes whose bones haven't been used and reused by another arist at some point in human history. Can you? Innovation occurs everywhere, for sure; everything keeps changing. But ultimately we're all equipped with the same notes and words, the same patterns to play with. It's not about finding something original; there isn't anything.
Keep breathing.
Because the beauty of knowing that nothing is original, is also understanding that everything is original. Because there is no one out there exactly like you.
I know, I know, this might seem cheesy, but bear with me, because it's actually quite stunning--
While all chord progressions have been rocked out on the guitar, they haven't been rocked out by YOU. They haven't been given your flavor and pace. While the theme of the heroic journey has been explored, killed, and then resurrected again for centuries, the journey has yet to be described and transmuted by ME. With my twists, my vision, my flare. My expression precedes me, it morphs my words, and textures my inflections without me even trying.