And the muse, being metaphorical herself, can come up with a number for the work of writing as well as the matter. (Though, like all analogies, they are imprecise; a precise metaphor would cease to be a metaphor and become an identity.)
Ideas -- ideas are sparkling little gems that need to have a piece of jewelry built around them. Though it often works best if you try to build more than one idea into the piece. It helps with length, and it keeps down the number of pieces you work on at once. Not always possible, because ideas are of varying stickiness -- some will cling together ferociously and produce a novel, and others are like ball bearings and produce a short-short.
And sometimes they, despite all appearances, are not ideas; they are half ideas, and when they met their other half, they click together like puzzle pieces.
Of course, there's more to the matter than the original idea. There's also that extremely salty sea, the imagination, in which you carefully dissolve stuff -- great masses of stuff, with no notion of when it will be used. Sometimes it gets supersaturated, and when an idea nucleus hits it, it crystallizes around it so quickly that you can't remember what parts were first and what later.
Outlining is like plunging into a valley full of mist, where you can see only a handful of trees and maybe the other side, and blazing a path through it so that a full blown hiking trail can be built.
Writing is, of course, like building that trail, and finding places where the footing is not as sound as it appeared, or a particular sight is a few feet off the trail so it really ought to be included. And even where the blaze is sound, you have to build a good stout path. OTOH, the story is also like a rose bush that puts out sprouts as swiftly as the ones about Sleeping Beauty's castle, sometimes (not always, fortunately, or the subplots would ensure it would never end), and you have to build a trellis and train it over it. . . .and sometimes you have to put it on the backburner to bubble together a little longer.
Then you have to put it aside to cool, which can also, it sometimes turns out, be putting it on the backburner to bubble a little longer.
And revising is like going into a garden with shears to cut off the deadwood and new sprouts to plant in bald spaces, and training some vines over trellises and pulling off dead leaves and flowers off others.