To begin, I should warn any Star Trek fans who may have followed a link, that this post has nothing to do with the only Russian crew member of the Starship Enterprise. It does however, involve another Russian - Anton Chekhov, author and dramatist who came up with a principle that is regarded highly in any form of story telling.
In short, Chekhov's Gun is the principle that a narrative should contain only elements that are absolutely essential to the plot and nothing else. Why the gun metaphor? Well, if a gun is mentioned in Chapter one, then at some point following, said gun must be fired otherwise it has no place in the story at all. It is useless, surplus to requirements and should never have been included as it makes a promise to the reader that is not honoured.
Of course, to say that every gun must be fired is to misunderstand the principle. Say for example, that two characters are involved in a business meeting. One of the characters owes the other money and has come into his office to plead for more time. The money lender is seated behind a large desk, upon which a gun is visible. In this instance, the gun is serving a purpose as it threatens the character who owes the money and it does not need to be fired in order to perform its duty to the plot. The principle applies only when the gun has no obvious bearing on the plot. The classic example is the one that places two characters meeting in a room and the narrator mentions a hunting rifle hanging on a wall. In this instance, the gun is not serving a purpose, it is merely a decoration. Unless, at some point, one of the characters is going to use that gun, it has no business hanging on the wall.
The technique is most useful as a form of foreshadowing. To avoid unlikely coincidence and to make a plot believable, foreshadowing is an essential part of the writing process. An example of the Chekhov's Gun principle in my first novel can be evidenced during a scene about a third of the way in. A group of characters hatch a plot to rob the storeroom of the bar where they are staying. A crate of vodka is taken and stashed under a caravan. This has no obvious relevance at that point in the story, as it does not really have any bearing on the characters ability to partake in the consumption of alcohol. They had access to drinks before they stole the items and they have access to alternate sources after. There was however, a very good reason for having a crate of vodka placed under the caravan, which you will have to read the book to discover (to tell, would be a major spoiler).
The obvious question is that if everything has to have a purpose, how does this affect the author's ability to place red herrings into the story. Could an object simply having the purpose to create a red herring be reason enough to include it in the plot? This is a tricky question to answer and I would have to say no. My reasoning is that a writer should never try to deceive or mislead their readers directly. It confuses them and a confused reader is not a satisfied reader. Intrigue - good, confusion - bad.
So how do you create a red herring or perform an unexpected twist to the ending if you are being open and honest with your reader at all times?
The answer is that you use your characters. By all means, feel free to mislead, cheat and deceive your characters, through whose eyes the story is distilled. If through the characters failings or limitations they are led down a misleading path, the reader will accept this much more kindly than if they had been lied to directly by a dishonest narrator. (I must note here, that I make a huge distinction between a dishonest narrator and an unreliable narrator. The unreliable narrator is a technique used in stories written in the first person and any mis-truths are the result of the narrator character's failings or agenda and are central to the plot. A dishonest narrator would be a third person story, where the author, not a character, attempts to provide a twist by misleading the reader through the mechanics of their writing as opposed to weaving the twist into the plot, as it should be done.)
To summarise, I believe that the principle of Chekhov's Gun is a powerful one and should be adhered to. When you build a house you do not add more rooms than are required and so it is with writing a book. Describe only that what is essential and avoid unlikely coincidence. Above all, never, ever, lie to your readers. If they ask "why did the author mention that" and you do not tell them, then you are going to be in major trouble.