I'm a native speaker/writer in English, and write my own content from website articles to a published book of my own. I have many years of experience writing, and editing other people's work. I've studied many topics during my years in college, and earned a Bachelor's degree in Psychology. It's very important to have a fresh set of eyes to edit your content because you expect certain words to be there. You know the meaning behind what you're saying. However, that fresh set of eyes isn't linked to your brain, so the editor will find any possible errors that your brain has hidden from you.