This chapter of Bird by Bird gives us the story of the title of the book. And that's an important thing for a writer to remember. There are times when I get myself bogged down thinking things like I need 20,000 more words or I need 6 more chapters and so I dither. The answer to this is to think in small units.
I can write a paragraph and when that's done I can write another one and suddenly I have a scene and this becomes a chapter. Taking a story bit by bit is a good way to keep from feeling pressured by yourself. Of course sometimes the floodgates open and words pour out. There's nothing wrong with this either.
One thing I tell new writers and that's to write every day even if it's only a paragraph. At the end of the week maybe you'll only have seven paragraphs but chances are the next week the writer can produce two a day. Suddenly they have a whole page and do a page a day. This comes to 365 pages a year and many books are that length.
The moral of this chapter in Bird By Bird is to think in small units and the large unit will happen.