Motive is a fundamental element of any work of fiction. In crime writing, the criminal’s motive is always one of the factors that single him out. Although in classic detective fiction there is usually more than one person with a possible motive. But in any situation, in order to make things real, it is necessary to understand why did the protagonist say those words, do those things? What motivated him or her?

And that means that we writers have to have some understanding of psychology. And, because human psychology is so complex, we have to avoid the obvious. Jealousy, greed, bigotry, are all things that make people behave irrationally. But rarely, in real life, are those emotions the only driving force behind someone’s behaviour. People are not always consistent. They might get angry because they see a lover with someone yet be so besotted they convince themselves that what they are witnessing is innocent. They suppress their anger. Until they discover they were mistaken, whereupon the anger erupts much more explosively.

Or they completely miss-read what they witness. In Ian McEwan’s Atonement, a child’s interpretation of something she sees leads to a lifetime of jealousy and hate.

Complex motives are central to the genre of psychological thriller. Whereas in a detective story the villain’s motive is withheld until near the end, forming an important part of the denoument, in the psychological thriller motive is revealed early on. Tension is built on the fact of the reader being privy to the villain’s devious reasoning. The reader is on tenterhooks, watching the victim fall into the villain’s trap, unaware of what lies in store.

Sometimes we ascribe motives that require deeper analysis. If an abuser blames the fact that he was himself abused as a child, we have to ask why did the earlier abuse take place. How far back might such a chain of responsibility go? And it is not only personal motives that need to be examined in some situations. Institutions have reputations to protect and that can often lead them to make decisions they later regret.

Can you think of examples of stories in which the explanation for a protagonist’s extraordinary behaviour was unexpected yet perfectly plausible? This might be from real life or from a fictional work.