Short stories must tell the beginning, middle and end of a story quicker than novels, and the best endings are ones that have a twist at the end. Twists, such as the storyteller being the villain instead of the hero or the narrator being dead, surprise readers.
Telling a good story, especially a short story, with a surprising twist at the end requires the writer to lead the readers to one conclusion about the story, and then take them in a completely different and shocking direction. One of the best ways to do this is to employ a style called the "unreliable narrator." This means that the writer uses one of the main characters of the story to weave a tale that seems to be going in one direction. By the end of the story, this unreliable narrator ends up taking the tale in an entirely different direction.
Having the narrator be dead or the villain in the story can take the story in a number of new and inventive ways. If the story is about everyone living through an ordeal, finding out in the end that everyone actually died can be the ultimate twist. The same type of shocking twist is achieved by making the storyteller the bad guy.