My Personal Blog
It does not matter how good a writer you are or how easily the words flowed when you started putting them down on paper. You should have someone else read it before you even think about sharing it with the world. Whether you write novels, fanfiction, or poetry, having somebody who can give you feedback can be the difference between a few sales and a bestselling breakout.
When you write, you are just too close to it to see the sometimes nitpicky little flaws that will throw your reader right out of the story. Those tiny flaws exist even after you have taken breaks and gone through a round or three of editing. Hopefully, you have already caught the simple problems of missing or wrong words or accidental changes of tense or point of view before you get to this point. It is still entirely possible that you have missed some of these things.