The achievement or failure to achieve the goal is an important but short moment at the end of the story.  So how is interest maintained over the course of the story?  By the progress of the quest toward the goal.  This progress is measured by how many of the requirements have been met and how many remain.

Requirements can be specific, such as needing to obtain five lost rubies that fit in the idol and unlock the door to the treasure.  Or, they can be nebulous, such as needing to reach three progressive states of enlightenment before the dimensional portal will open.