Motivation is a key-concept in psychology and in fiction. It is a man’s basic
premises and values that form his character and move him to action—and in
order to understand a man’s character, it is the motivation behind his actions
that we must understand. To know “what makes a man tick,” we must ask: “What is
he after?”
To re-create the reality of his characters, to make both their nature and their
actions intelligible, it is their motivation that a writer has to reveal. He
may do it gradually, revealing it bit by bit, building up the evidence as the
story progresses, but at the end of the novel the reader must know why the
characters did the things they did.