Teen age girls will sometimes lie to avoid getting into trouble, especially if trouble involves a whipping.Also predictable, it is easier to keep a lie going once it gains momentum than to confess that you've lied and deal with the consequences of your actions. This is especially true when you have lied in the first place to avoid taking responsibility for your actions, and have tried to avoid the consequences.
Perhaps the most predictable actions were when Abigail accused Elizabeth Proctor, and again when she accused Mary Warren. The first was simply to clear the way for her and John Proctor, and the second was simply self preservation. By discrediting Mary, she was also saving the reputation of herself and the other girls.
In the middle (predictable and unpredictable) is what happened with the townspeople. The part that is predictable is that the townspeople were mostly uneducated and superstitous. The devil was real to them and they could believe that the devil was at work because they had been indoctrinated to believe it. What was unpredictable with the townspeople was how quick they all were to confess, especially given that they were a people who took lying very seriously.
With the townspeople, the predictable elements were those where people acted in consistency with their character. Some people, the Putnamn's for instance, saw an opportunity to gain and they took it. They were basically unloving people from the start, so their actions were consistent with their personality. Similarily, the characters who refuse to confess in order to protect their honour are also predictable, at least from within the perspective of the culture they come from. They would consider themselves damned if they lied, so from their perspective, they were giving up their mortal lives to save their immortal ones, their souls.
Unpredictable elements are the ones where people said or did things that they didn't expect to turn into trouble. For instance, when Giles Corey mentioned his wife reading, he would never have thought that it would get her arrested. Similarily, when Proctor said that Elizabeth couldn't lie and she lied to protect him, neither of them knew that it would damn them both.