Re: Don't get it
>>> The issue here is how much actual physical prose will carry over from one version to the next. In a novel, huge chunks can be reused. With a short story, you must begin again from scratch. <<<
The pie comparison is silly; attempts to explain the analogy border on ludicrous. A story, unlike a pie, isn't 'completely ruined' by one bad or missing ingredient. I recently read a manuscript which was excellent, except for one flaw. The writer started the story about 500-600 words too soon. Very little will be needed in the way of rewriting to fix that story. Heck, it would probably sell if the writer simply threw away the first page. Likewise, I've seen cases where the writer dropped the ball on the last page, or even in the final paragraph. Again, not much needed to fix those stories.
This whole pie thing seems to be a crude way of saying, "Write novels. Don't bother with stories." I think Mr. MacDonald's opinion is just that, an opinion, and in this case one I don't agree with. A novel, more than a story, needs a strong foundation and solid framework. A story can squeak by on a good idea or a strong character. If, somewhere around page 300, the novelist discovers he's been barking up the wrong tree the whole time, he can't slap on a Bandaid adhesive bandage and fix it.
If you believe that a story can only be 'fixed' by completely rewriting it, you're basically saying that every story problem has to have catastrophic results. You are saying that it's impossible to write a good half of a story but screw up the second half. Sometimes it's easier to rewrite a story than it is to cannabalize its good parts, but that doesn't mean that every 'failed' story needs to be competely rewritten.
In fact, that sounds like a recipe for failure. Editor #1 rejects my story. I rewrite. Editor #2 rejects my story. I rewrite. Sooner or later, anything that was good in my story is completely gone.
In a workshop, if you receive 20 crits on a story, half of them will say it just needs tweaking and half will say it needs rewriting. Several people will say it's the best manuscript they've ever read, and several will say it's the worst. Three people will point out a particular line and say they wished they'd written it. Two people will point to that same line and tell you it was clever but didn't fit the story. As writers, we have only what we have written. My advice is, be ready to cut or change anything, but don't throw out a single word carelessly, and only revise what feels wrong to you.