Write 100 (or so) words about whatever is on your mind. Don’t think about it; just write 100 (or so) words.
Put those 100 words away somewhere safe where you can’t see them. Done? Ok, write the same 100 words you just wrote again. No cheating. Not the exact same words, but the same words.
Put the two drafts next to each other and write down how they are different.
The first critical realization is, “I can write.” You don’t need to believe that fully to begin writing, and the final realization will take years to discover.
The second critical realization is, “I am required to edit.” Like the first realization, you realize this slowly and painfully because tearing down the words you just painstakingly produced seems counter-intuitive. Why is tearing it apart the first thing I do when I’m done?
I’m not going to answer that question yet. I will start by showing how the same bit of writing is affected by considering it. If you completed the exercise, was the second attempt better or worse? Shorter or longer? Why? My answer is you took more time to consider what you were writing.
There are two parties that you need to cultivate as editors. You don’t need the second party yet; it’s an external editor, a human who is not you. Their job is not copy editing; it’s editing of the work. How does it sound? How does it feel? Does it sound like you? Does the thought make sense? What needs to change in the piece to allow it to be clearer? More descriptive? More thoughtful.
The first party is you. Yes, the work feels precious at the piece’s inception, but look what happened when you wrote the same piece twice. See how your brain considers the same thought with different words? This is because you already knew the piece and weren’t writing; you were editing.