This is good advice, but I've seen huge successes by authors and article writers who violate these rules (the recent trend of long literary fiction such as 'City on Fire', which is 900 pages). Nowadays, the trend is towards longer, 'epic' fiction with post-modern themes, whereas in Vonnegut's day (along with Heinlein, Asimov etc.) 'short' was better. Up until as recently as the 90's, 'short' was ideal, but all that changed. Look at Harry Potter and other popular books...all very long. It also deepens on the audience and the purpose...if you're trying to convey technical information , fluff is undesirable
I think authors from the 50’s/60’s/70’s often wrote shorter books because they worked their way up writing for pulps and magazines. After the market for that stuff dried up authors seemed to start writing more open ended stories.
I read Slaughterhouse Five recently and I dunno. Maybe I'm burned out on WW2 or maybe I'm lowbrow, but mostly I was bored. Guy has a bad wartime experience and then goes crazy and something about aliens, I guess. OK, on to the next book.
Slaughterhouse Five has been my least favorite Vonnegut that I've read. However, I've absolutely loved the other few that I've read, most recently Cat's Cradle.
With writing, music, and perhaps even software it is best to know and understand the rules and be able to use them before you start breaking them. When you do, you'll know why and do so for a purpose.
His advice has nothing to do with page count. I imagine that he would think Anna Karenina a work of genius. The book he recommends at the end, The Elements of Style, goes into more detail about exactly how to prune. Here's one of its popular quotes:
"Vigorous writing is concise. A sentence should contain no unnecessary words, a paragraph no unnecessary sentences, for the same reason that a drawing should have no unnecessary lines and a machine no unnecessary parts. This requires not that the writer make all his sentences short, or that he avoid all detail and treat his subjects only in outline, but that every word tell."
Of course that just is an introduction. The books goes on with many guidelines and lots of examples that really made it sink in for me.
Bad writers don't follow the rules. Good writers follow all the rules. Great writers know which rules to break when, and why, and have good reasons for doing so.
That trend is absolutely normal and except Harry Potter nothing else is good literature. And Harry Potter is only good literature because it is a great story, a really good adventure epic. The rest are mere products, completely forgettable, in the same way modern pop is not going to be remembered through generations.
Those Russian guys were writing pretty big novels 150 years ago too, though. I will say that War and Peace was a much faster read (at least for me) than Infinite Jest - though I greatly enjoyed both, in very different ways.
The problem for me with Harry Potter, is that it's ALL from his viewpoint. If Harry didn't see it happen, then it didn't happen. There's absolutely no other point of view presented in the novels, and the final two are just simply written diarrhea, with a rushed 'blink and you miss it' ending.
Mechanically, it doesn't work for the reader to inhabit the head of, say, Dumbledore. First, Harry as outsider lets the author introduce new concepts like magic gently and slowly so it's relatable to the reader, and secondly part of the reason you choose first-person perspective is that it lets you keep the audience unaware of the big picture until you want them to see it.
Latter day Heinlein novels are anything but short. And very rambling - still sold in droves though, and are mostly good reads, but nowhere near as sharp and observational as his early work.
I'd like to see a return to the sub-200 page novel. Nice quick reads, one-shot stories, for when you tire of yet another 10 book epic.
I've heard it said now, that Publishers won't even consider your manuscript unless you've already got another two completed sequels in your back pocket. It's all about the money.