In art there are no absolutes like in management you can always find good examples proving the principles wrong. The principle is more a guideline for new writ

In art there are no absolutes like in management you can always find good examples proving the principles wrong. The principle is more a guideline for new writers not to ramble and maintain focus especially if there are word limit restrictions typical to published short stories of the era, you cannot afford to waste words on things that don't matter to the story. Established authors like Hemmingway or Asimov can get published with shaggy dog stories most regular authors cannot. Even those authors can get a way once in a while, however most of the time they too have to follow the principle like everyone else too.