I remember a movie about a writer who frequently ended his program with a cliffhanger that looked impossible for his characters to get out of. The next week the character would be miraculously saved. One episode ended with the character falling from a plane without a parachute. The following week he was rescued by landing on a bird in flight. This raises three questions about validity. 1) Was this coincidence or divine intervention? Not coincidence. 2) Could this really have happened? No. 3) Do we live in a cartoon world? The world isn't Toon Town; when you fall out of a plane, that's all folks.
We could have God fix everything. All we have to do is reach the point where we don't know how to end the story, then have God reach down and set it right. But the last three times I called down fire from Heaven, it didn't work, so I think Divine intervention in stories is just a copout for "I couldn't think of an ending." Whatever you have to say, better let God send His own messages.
The Hand of God often shows up as some coincidence that makes the story work, when normally it wouldn't have. It's having a thirty-nine-inch car show up just in the nick of time. It's having it rain just in time. It's Aunt Louise dying and leaving an inheritance just in time.
When God isn't the excuse, the writer's hand is. For example, a traveling man on a train has a series of chance encounters with three different people who bungle around and get him in trouble. In comedy it might work, but not drama. Why? What are the real chances of meeting one person who gets you in trouble? It does happen. Two people - highly unlikely. Three - forget it. Too much coincidence is the mark of a story which has been fully manipulated by the writer.
Where do you draw the line between plotting a story and contriving it? Plotting should be the intelligent foresight of what should happen, given the characters and situation. Contriving is arranging outside events to manipulate the character. In a normal story, the characters create their own destiny by their own actions. The antagonist throws everything he can at the good guy. The protagonist fights back with all the strength and wits he has, using all the resources at his disposal.
For example, story YZ is set at a munitions factory that makes conventional bombs, tucked into a small hamlet in rural Pennsylvania, in a very hilly, well forested area. Turk is a munitions manufacturer and arms the bombs. His assistant, Fanny Brightenberry, assembles the arming mechanisms and tests them. Fanny, desperately needing money for her kids education, gets recruited by a hostile country to supply information. Turk notices her copying documents and begins to spy on her. She is informed Turk is on to her and is told to be more careful. Turk sets a trap for her and confronts her red handed. She threatens to blow them up and the entire factory. He talks her out of it and secretly helps get her out of trouble with the foreigners. All of this would be relatively within reason.
How would a contrived story look? At the munitions factory, Fanny gets recruited. Turk "senses" something is up and gets suspicious. He watches her. She steals the information and he follows her to a drop site. Turk confronts her, but she has been trained in a special Middle East terrorist camp (we now learn) and drowns him in a nearby river. He survives and arrives at the factory in the nick of time to prevent her from escaping with all the documents. He is secretly ex-CIA (we now learn). He holds her at gun point and calls the local Sheriff. The Sheriff enters, but he is in cahoots with Fanny (we now learn) and disables Turk. Fanny heads for the company jet (wasn't in the original - too hilly and company too small), carrying with her a nuclear bomb she just happens to have access to (factory originally made only conventional weapons), and just happens to know how to load it on the plane and how to fly a jet. Turk, of course, has had flight training. He goes up in a friend's jet and forces Fanny to land while convincing her over the radio that all will be well.
To write the contrived synopsis, I ignored half my intelligence (which isn't hard for me) and just put down anything convenient to make the story do something exciting. At the right times, Turk is suddenly able to sense things, Fanny is suddenly terrorist trained, Turk is suddenly ex-CIA, the Sheriff is suddenly in cahoots with Fanny, Fanny can suddenly fly a jet, the company suddenly has a jet, the company suddenly has a nuclear bomb, Fanny suddenly knows how to load a nuclear bomb, Turk can suddenly fly a jet like a fighter pilot, and Turk's friend suddenly has a jet. Good in another setting, but all totally unbelievable in this one.
1) Establish a realistic setting with only specific resources. Create character profiles and stick with them. Allow your characters to use only the resources at hand.
2) Your characters must be the instruments of their own destiny.
3) The things your characters do must be believable. The plot must follow an intelligent path.