When a Normal Screw-up Just Won't Do

This is Mr. Wrenchy. He has plans for your characters. Diabolical, horrible, awful, TERRIBLE plans. But there's a condition...you have to throw him.

We writers play a cruel game with our characters. We know what they want, and we know exactly how they can get it. Most of the time, it's pretty simple.

This, ladies and gentlemen, is why the author has an endless supply of wrenches we can chuck into any situation.

Wrenches can be big things: Explosions, viruses, death, mayhem. 

Sometimes wrenches are small things: Forlorn look, a careless dismissal during a crisis time, selfishness. 

Wrenches can be subtle, or they can hit your characters upside the head and knock them unconscious for a few days. 

I like to use a mix of the big ones and the small ones. I have a scene in Spark where one of the MCs is trying to convince her dead hubby's spirit to "cross over" and finally be at peace (long story). When she's on the brink of getting him to cross, his attention drifts for a split-second, and his desire to cross is lost. It's a small wrench that has big implications in Book2. 

Characters have to struggle to get what they want. People don't fit into an infinite mold of "will do what you want" and "won't do what you want." There are a lot of factors that play into a person's choices--motivations, personalities, likes and dislikes, and it's up to you, the author, to play with these different aspects to craft appropriate wrenches.