If you want to make writing into something that disappoints and defeats you at every turn, here's how to do it.
Set high expectations.
High expectations increase the stakes in your writing. They take what should be an engrossing, fun process and turn it into drudgery.
High expectations subject you to your ego, and of course your ego (in concert with your internal editor) always measures your writing before it's ready and censors your thoughts before they form.
High expectations will keep you from writing well. They may keep you from writing at all.
Just sit down and write, and don't have any expectations at all. It's yet another of the cruel ironies of writing, but that's when your best work will come out.