Why a million words? Ten books of 100,000 words each? Really? The answer is YES!
It takes a million words to find your voice. Before I published anything I wrote over a dozen books. Now I’m up near 15 or 16 books, with only 3 of them published. Maybe there are people that can master it faster than I did. But my experience backs up what Bradbury said. It took a long time to write anything decent. It took me over a decade to learn world building and character development.
It’s probably worth mentioning that some people, like J. R. R. Tolkien, get their million words by writing the same story over and over.
From another source I heard it takes over ten-thousand hours to master any skill. That means an average of only 100 words per hour. That can’t be right! But think again. In addition to writing book after book, any serious author is also going to read books on how to write (see source above for an example) and attend classes and/or conferences and/or conventions. I also recommend The Author’s Tookit, and On Writing by Stephen King. Don’t forget grammar books like The Elements of Style. Here’s The Art of Writing by Robert Louis Stevenson.
Whenever an author finishes a book, they ask what to do next. The answer is, study how to write, then write another book. Publishers aren’t interested in one-hit-wonders. They want to invest in authors who will be producing books for the rest of their lives. When you get there, you can always go back and rewrite (one of the most important skills, and it doesn’t increase your word count at all) the first books. If you love writing, the thought of writing a million words is not daunting– because you know you’ll be writing for the next ten years and then for decades after. It’s been said that everybody has a book in them. I guess the difference between authors and everybody else is that authors have more than a dozen books in them.