Michael Agger looks at scientific studies on writing to figure out why it’s so damn hard:

Kellogg terms the highest level of writing as “knowledge-crafting.” In that state, the writer’s brain is juggling three things: the actual text, what you plan to say next, and — most crucially — theories of how your imagined readership will interpret what’s being written. A highly skilled writer can simultaneously be a writer, editor, and audience.

All that mental shifting slows writers down.

Since writing is such a cognitively intense task, the key to becoming faster is to develop strategies to make writing literally less mind-blowing. Growing up, we all become speedier writers when our penmanship becomes automatic and we no longer have to think consciously about subject-verb agreement.

I can attest to screenwriting getting easier and faster with practice. The form is so esoteric and strange, with special formatting and rules to follow, that the first few scripts you write are mostly about getting comfortable with the shape of screenplays.

Once you start to recognize the rhythm of the page — how action interrupts dialogue, how to change locations while staying in a story thread — a lot of the frustrating craft stuff melts away. Decisions you used to consciously agonize over get taken care of before you’re even aware of them.

(Or, more geekily, it’s like your brain develops a graphics card to ease the strain on your main processor.)

I really notice the difference when I write prose fiction. I’m happy with both The Variant and Snake People, but they were exhausting to write, because I found myself far too conscious of every choice.