This is one of the essential elements of fiction writing. Everything relies upon cause and effect to maintain the story and characters' forward flow to the end. It follows along the line of "for every action made another action is created." You must have this in your story, otherwise, it doesn't go anywhere! Effects, or shall we say plot developments, must have causes, or background, to exist.
Example: In Harry Potter and the Chamber of Secrets, during the dueling scene the students are horrified when Harry tells the snake to leave Justin Finch-Fletchley alone. The snake's approach upon Justin is halted by Harry speaking to it. This is the effect. Yet why does the snake leave Justin alone when Harry tells it too, when it is clearly enraged at its handling and on the defense? Why would the students be horrified that Harry saves Justin from a snake bite? Because Harry unknowingly spoke an incomprehensible to humans language, Parseltongue, and did not comprehend he'd done so. This is the cause. Later the students treat Harry with distrust and more fear to the point of paranoia. This is further effect from the action of Harry speaking Parseltongue.
Blind luck, fate or coincidence is difficult to uphold in fiction. Everything must be greatly exaggerated or explained to make it seem real life to the reader. You can't just have the character energetic and healthy one day and sick as a dog the next day. You must show how the illness happened to make it believable. Perhaps the character is overworked or works in a germ-filled environment? Perhaps everyone else around the character has the flu and its just inevitable that he/she will get it too. But you MUST SHOW IT. Have fellow coworkers coughing, sneezing, and blowing their noses as your character interacts with them. Then when your character wakes up feeling like the living dead, your readers can go, "See? Should not have associated with all those sick people!" Plus it would explain why your character saw but did not comprehend the importance of a certain clue or something else intrigal to the story's continued flow. The reader still has the information as does the character but the character, due to being ill and fuzzy-brained, doesn't comprehend the importance of that clue until later when they are a bit clearer of mind. Cause and effect helps suspend the reader's sense of disbelief and makes everything more believable or understandable.
Cause and effect can also be called stimulous and response. While cause and effect are more long term and far reaching into your story, stimulous and response is the right now, this instant. To make this understood more, a few simple rules should be kept in mind:
-Stimulous must be external -- everything must be witnessed by the reader as if it were on a stage. -The response too must be external in a similar fashion. -For every stimulous, there must be a response. Kind of like for every action there is an equal (though not always opposite) reaction. -Response must follow stimulous immediately, while effect can happen a bit further down the line from the cause, though it must be clear the cause is what created the effect. -When response is not logical on the surface, you must explain it.
The book I took all this from Scene and Structure by Jack Bickman has some great examples of stimulous and response. Forgive me for snatching them.
Joe threw the ball.
Now the reader will expect to see in words the following happen: Sam will either catch the ball, not catch the ball, or didn't see it and got bashed in the nose as a result. The reader will be very confused if Sam begins making conversation about the weather instead. The question raised will be "what happened to the ball?" Very confusing and happens often, especially in fan fiction. The writer assumes that the reader will understand that Sam caught the ball and began making conversation. This cannot be done. The best way to mix this is to have Joe throw the ball and Sam catch it while saying "It's a nice day to play catch."
Another common mistake in fan fiction is the following: Mary walked into the party. "Oh no!" groaned Julie, and she ran for the exit.
While its obvious that Julie wants nothing to do with Mary and Mary's entrance cause Julie to flee, the reason for Julie's sudden departure is completely unexplained. The writer assumes that the reader will understand that either the two girls are wearing an identical dress or that they do not like each other. Wrong. A bit of background or explanation regarding this situation is usually ignored and thus confusion reigns.
Stimulous and response can also be easily messed up. Too much time between stimulous and the response can mess up the timing very much. A character getting angry three days after an incident, for example. Why get mad three days later for getting a parking ticket you've already paid? You can destroy the credibility of stimulous and response three ways:
-No response to the stimulous at all. The character's father passes away but the character has no reaction whatsoever, ignores the incident completely even though he/she attends the funeral and everything. The character acts like its an everyday occurrence. -No stimulous to a response. The character begins crying uncontrollably yet no reason is given why this has just suddenly occurred. -Too much story time passes between the stimulous and the response that the two events no longer have a connection. To go back to Julie and Mary at the party, earlier in the story the author mentions in seperate scenes that Mary and Julie both put on blue dresses with white lace trim. Two chapters later Mary enters the party and Julie suddenly cries "oh no" and runs off. Yet in the meantime, Mary's car has broken down, making her late and Julie discovered the punch is poisoned.
JK Rowling is excellent at doing this next bit: internalization. Giving the character's internal thoughts regarding the stimulous or cause, thus giving an explanation or background to the response or effect. Harry does a lot of internalization as he goes through his new life as a wizard.
Internalization works like this. I'm doing this from Lucius Malfoy's point of view in the office of Dumbledore scene in the Chamber of Secrets.
"Well, you see, Lucius," Dumbledore said, smiling serenely," the other eleven governors contacted me today. It ws something like being caught in a hailstorm of owls, to tell the truth. They'd heard that Arthur Weasley's daughter had been kille and wanted me back here at once. They seemed to think I was the best man for the job after all. Very strange tales they told me, too...Several of them seemed to think that you had threatened to curse their families if they didn't agree to suspend me in the first place."
Lucius froze and he could feel the blood drain from his face. Dumbledore was not a wizard to underestimate and just once Lucius had been positive that he'd managed to get the upper hand over the old geezer. Rage flamed through his body and it took a moment to control it lest he do something that was foolish. Dumbledore was a dangerous opponent and not one to be faced one on one. Besides, Lucius had always preferred his enemies with their backs turned. It wasn't honorable but it was almost a sure victory. Winning was everything, he knew, if one wanted to maintain control in this world.
Deciding to change the subject he sneered, "So--have you stopped the attacks yet? Have you caught the culprit?"
"We have," Dumbledore smiled at him.
Cold replaced the heat of anger. What if Dumbledore could prove that he'd dropped the old diary in little Weasley's cauldron? No, he told himself mentally, not possible. No one even knew of its existance, let alone have the ability to trace it to Lucius Malfoy. Let Dumbledore suspect all he wants, he can do nothing if he can't prove it.
"Well?" he said sharply when Dumbledore elaborated no further. "Who was it?"
"The same person as last time, Lucius," said Dumbledore. "But this time, Lord Voldemort was acting through somebody else." Lucius took a steadying breath, hoping his nervousness at being caught didn't show. "By means of this diary."
The old man held up the familiar black book that now had a large hole in the center and was scrutinizing Lucius closely. Lucius struggled to maintain his composure and was certain he'd succeeded. Those damned eyes of Dumbledore were unnerving, though, and it was difficult to keep his composure under their peircing gaze.
As you can see, a lot more of Malfoy's reactions to Dumbledore's words are explained by Malfoy's internal reasoning and thought.
The use of both cause and effect and stimulous and response is essential to crafting the plot and maintaining the structure of a good story. Without them, it would literally be uninteresting and fall apart.