If you hear the constant litanies of "Be sure you capitalize," "Dot your i's and cross your t's" and "Don't start a sentence with a preposition," then it's time to deconstruct the varying voices of past experiences.
Any time we stop ourselves from writing based on a myopic view of this wondrous adventure, we put ourselves back into that classroom of rights and wrongs, do and don't and succeed or fail. Notice how judgmental and grating that voice is in your head. Do you give it a male or female voice? Is it high-pitched shrieking or a silky appeal to the editor in you to: "Make this madness stop!"
Take a deep breath and look around at the numerous tomes on writing that surround you. I've spent hundreds on books alone, much less the college and online writing courses that have included everything from the art to the business of writing. But as a writer, each book and class made me believe deep down that only the privileged few could reach the heights and put out books that are "worthy."
That is why I'm still editing my first young adult science fiction book, which has been completed for at least three years. It is in part why another book that is near and dear to my heart is only at three chapters. I listened to that editor and teacher in my head, rather than believing in the simple truth of those words, the characters and the worlds that are mine alone and worthy.