on Writing Forward:
Those of us who spend a lot of time studying the craft of writing inevitably come across bits of writing advice that we hear over and over again: show don’t tell, write what you know, and kill your darlings. These writing tips can be a bit cryptic, but the one about revisions is crystal clear: writing is rewriting.
The intention is to get ideas out of your head and onto the page (or the screen, as the case may be) as quickly as possible without worrying about grammar, spelling, and punctuation. You don’t need to get the details right. Just get that rough draft completed. You can clean it up later.
Like most writing tips, this one is debatable. Some writers prefer to labor over each sentence while composing a first draft. This means fewer edits later. Others use the drafting process to navigate through their ideas. This often means more revisions when the drafting is done; in other words, the bulk of time is spent on rewriting.