That could well be the most often repeated advice for writers. Rubbish, I say. Poppycock. Also, bushwah. (Which I believe is the sound made by Pretend President Georgette when he doesn't get his way.)
It's not that the rule is inherently silly but rather that, as is often the case with occasionally useful rules, it leads to silliness if it's followed in all circumstances. Some rules really are made to be broken.
Surely no one would write
John placed his hands on the arms of the chair and exerted downward pressure, simultaneously leaning forward and straightening his legs. Then he straightened his back. Thus he brought himself to a standing position. Once he was standing, John raised his right foot slightly, leaned forward, and placed his right foot down on the floor a few inches ahead of him. Moving steadily, he then raised his left foot, which was now behind him, advanced it to a position a few inches ahed of him, and ...
instead of
John left the room.
Arguably, the second version is telling, while the first is showing. But of course we all do that all the time in our writing. What matters is choosing what to show and what to tell.
What prompted these rather obvious thoughts was this. Recently (April 2007), I was revising my novel in progress,
Time and the Soldier, and I was horrified by the crapociousness, the crapulosity, in short the boring, dreary awfulness of one long section of the novel. (The rest is brilliant!) Thinking - well, obssessing - about it later, I realized that that section of the novel was crapocious precisely because it consisted of boring and irrelevant showing. What happens in that part of the book is relevant to the story, but how it happens isn't. So I decided that on some future pass through the ms., I would chop that part out with a meat cleaver and replace it with a very brief bit of telling. The book would be much improved.
And the world would rejoice. Well, I would.
Or maybe this is the advice most often given to writers. Thank God no one worth reading follows it.
If they did, we'd have very little genre fiction. Almost all fiction would be mainstream and would mirror the writers' lives, which means it would mirror our own lives, and so fiction would no longer serve its main function, which is to enable us to escape from our tedious, boring, pointless, aimless lives for a few hours.
God, do you realize how much of that mainstream fiction would be written by college English professors and would be all about college English professors having midlife crises? Aaaaiiiieeeee!
This rule becomes a good one if restated as, "Try to know something about what you're writing about before you write it. Don't just make stuff up. Google is your friend." But that's pretty obvious, surely.
The exception is if you're writing about the pretend president, who is entirely a creation of some PR firm and not an actual human being at all. So anything you write about him, no matter how invented, is acceptable, in the same sense that the syllogism
Whenever John eats refried beans in the morning, it rains at 6 p.m. that evening.
John ate refried beans this morning.
Therefore it will rain at 6 p.m. this evening.
is valid even though it's absurd.