How we change what others think, feel, believe and do
A 'red herring' is a distraction that is generally intended to throw the reader (or story character) off the scent of the eventual reveal at the end of the story or segment.
Red herrings include the appearance of strangers who may offer apparent clues or ask questions that have no real importance to the story. They thus may appear as blind alleys that lead the reader astray, at least temporarily.
Red herrings may appear as mysteries and tensions that are explained by normal circumstances, such as when a person goes missing in suspicious circumstances but later turns out to have gone shopping.
This is particularly common in 'whodunnit' crime stories to help keep the reader guessing until the final scene where the real culprit is revealed.
The red herring may be made obvious and the reader may be led away when the hero or another character is also fooled by it.
The genius of Sherlock Holmes is sometimes shown in the way he is not distracted by red herrings that fools his partner Dr. Watson (and perhaps the reader).
If a reader guesses the story, they achieve premature closure and may well lose interest in the story, which thus loses its power.
There often is a tacit game between the author and reader in stories that is something akin to fishing. The author seeks to get the reader hooked and then slowly reel them in without the reader realizing what is actually being done to them. The red herring helps distract the reader during this process.
Over-done, the culprit becomes obvious as the person from whom all paths lead away and suspicion does not easily fall. Done well, there are subtle clues along the way that makes the reader think 'of course' when the final culprit is revealed.
Having the hero distracted by the red herring is a simple way to lead the reader, who assumes that the hero knows what they are doing. This also adds humanity to the hero who is shown to have common failings as well as heroic traits.
The term 'red herring' comes from the old use of a salted herring (which is red) in training hunting dogs. The well-trained dog would continue following a weaker fox scent rather than be distracted by the strong herring scent.