Now that I have your attention, I will qualify this post's title. "100 percent originality" is a myth. No one can be one hundred percent original regardless of their medium because so many people have come before you. "Standing on the shoulders of giants" as the saying goes. To find these giants, I will use an idea common to the culture of Ancient Rome.
Back in the days of the Roman Empire, there was little in the way of literary innovation or experimentation. This was because everyone though it was pointless. No one believed they could do epics better than Homer so no one tried. The idea was to meet that level through imitation.
Personally, I think this idea is absurd. I understand it but I believe it is defeatist and ultimately self-fulfilling. While I don't think I will surpass the talents of my favorite authors (not any time soon at any rate) it is a goal that drives me to improve. Nevertheless, I find writing is more fun when I add myself onto the chain they created rather than trying to make myself different for the sake of being different.
When I was in college, there was a random encounter with another student and for some reason I talked about my desire to write a fantasy novel. This student asked me what made mine "different from all the others" and I gave my response but I don't feel he believed me. Looking back, I wonder why he thought originality was the most important question to ask. Trying too hard to be different is a novice mistake. (To read about this idea in more detail, click here)
Tvtropes will illustrate my point.
TvTropes lists the conventions of storytelling and all the many works that have used them, from today all the way back to the oldest works we know of such as The Iliad, Epic of Gilgamesh, etc. As a result of this, the Troper Hive Mind has produced "just for fun" pages that deal with originality: The Tropeless Tale and The Zeroth Law of Trope Examples.
The Tropeless Tale is a thought experiment concerning a hypothetical author that tried to write a story without using tropes. He couldn't write a character on any point of the hero-villain spectrum and his plot couldn't be anywhere on the scale of Comedy-Tragedy; in fact, he couldn't write about characters or plot at all. He couldn't even write about formless nothing because there are tropes for that. In the end he decided that the challenge was impossible because even if he succeeded and wrote a story without tropes, the story would only create new tropes which means he would retroactively fail.
The Zeroth Law of Trope Examples is also known as "Shakespeare Did It First". The Bard wrote many plays and sonnets and other literary works and within them one can find any number of tropes. There's Lampshade Hanging, Villain Protagonist, and even a "Your Mom" joke. To further drive the point home, Shakespeare himself was not wholly original because he adapted much older stories or historical events.
Originality is a myth and this is a good thing. There's no need to excessively worry about originality; write the story you want to write. Of course, you shouldn't plagiarize or infringe on someone's copyright but there's nothing wrong with seeking inspiration or doing a homage. The bottom line is that 100 percent originality, while something to strive for, is an Impossible Task.
For other posts about originality see Inspirational Monday-TvTropes, Originality and Tradition and "Literary Innovation Is Not Always Good",