Writing is an act of narcissism. Only a true narcissist would presume anyone else would care about the stories, thoughts and ideas inside your head. Right?
And yet to be a competent writer, you have to be the opposite of a narcissist. In order to shape your writing so that it reaches your audience, you must climb out of your mind--and into the minds of your readers. You must adopt their perspective.
Most importantly, you must have the patience to go over every word, phrase and sentence, combing over everything to make sure unreadable sentences do not survive in the finished version of your work. You have to obsess over your writing so your readers don't suffer.
Among the set of people who are narcissistic enough to share their writing with the world, there are pitifully few capable of this second step.
That's why writing is difficult.