In the consumption of a novel, not every reader will have invested money but they will all have invested their time. It is this commitment that places demands on the author. The upshot of which: readers will put in the hours, providing the following is met: a) The crime is solved. b) The protagonist survives relatively unscathed. c) The bad guys get their comeuppance.
Breaking these rules is doable, but risky. Novel writers aim to cultivate a deep emotional attachment between the reader and their characters. This restricts what the author can get away with. Ultimately, good has to prevail. My point is this: The more time a reader invests, the more they will expect to be rewarded with the payoff, and that folks, means a happy ending.
Pssst, keep this to yourselves. Short stories are different, not all the rules apply.
The engine of the novel is the what happens next, each passage should be crafted with the purpose of keeping those pages turning. Short stories are concerned with the what happens now.
Authors of short stories can ultimately shock in any way they please. By all means kill off your heroes, reveal them as evil, or end with the bad guy becoming the true victim. But aren’t these twists familiar to novels? Nope, they break the formula, and are therefore rare and hard to pull off. Readers won’t accept a journey of trials and suffering only for your main character to be unmasked as the murdered. In a short story, you don’t even have to root for your hero, you just have to be interested in them. (Sit-coms are aware of this. Characters like Basil Fawlty, Blackadder and David Brent, work well in the short - 1/2 hour - format).
So short stories are easier to write than novels, right? Wrong.
Shorts are best set over a short period of time, usually an event, or in the case of crime writing, the crime itself. But crimes are concerned with much more than this. Predominantly, crime novels are about how the perpetrators are caught. But motive must be also explained and victims sympathized with etc…All of which is difficult in a short story. Your protagonist hasn’t the time to fail a few times, or overcome obstacles, before solving a case. There is only one pace to a short story. FAST. Writers of short stories and novels can be as different as a sprinter and a marathon runner. One is built for power, for full-throttle energy. The other is a master of pacing, tactics and timing (whilst holding enough back for a final burst).
Short stories can still follow the basics: The Hook, The Conflict, The Climax, The Resolution, but often they fail because they do just that!