And there are lots and lots of invention strategies to help writers generate, focus, test, and elaborate ideas. The myth of the perfect first draft constrains more than a few basic writers, but most writers know that writing evolves as copy is produced. Ideas that seemed concrete suddenly become vague. Language that sounded good before it was written suddenly suggests meanings you don't want to suggest. Paragraphs that seemed to be in a logical order no longer seem well organized.
Writers make discoveries as a result of writing, and consequently, they draft, and draft, and draft.
Most of us compare passages that we write with an ideal textual version of that passage, one based on our perception of how the text ought to read, and how other texts have been read by us. Some of us rehearse mentally before we touch the keyboard. Others try to write everything they think about a topic so that they can find out what they know or don't know, what they like and dislike, and build from there. Writers develop a sensitivity to the sound of their language, their choice of the structure of their composition, the clarity of their ideas, the support for their positions. Thinking evolves, language becomes precise and powerful.