Creating a strong narrative spine

A strong story hangs from the clear, simple spine of a consistent, though deepening goal. The protagonist refines his goal and his understanding of his goal changes, but he does not shift his focus from one distinct goal to another. To say this another way: the Act 3 goal emerges from the Act 2 goal. Or, to express this as a formula: Act 2 Goal + deeper understanding = Act 3 Goal.

In a strong story, all of the narrative steps clearly support the simple spine created by the evolving goal. One step builds upon another so that there is a sense of constant accumulation. In the Call to Adventure, for instance, the protagonist is invited to embark on a quest, the quest that he will pursue, in an ever-deepening way, throughout Acts 2 and 3.