Pacing is underrated in storytelling structure; story structure often wants to mirror everything and contrast everything, with “bringing everything back” being the best way to make moments pay off and “book ending” (meaning having the beginning be either exactly the same or exactly the opposite of the end) as the best way to make sure the story comes “full circle”.
But this makes pacing misleading. If there are four acts, it is still a good idea to make the second half nothing a direct deconstruction of the first half to make sure everything neatly returns and nothing in the plot wastes time, but this implies that there must be the same about of moments in both acts. There are the same amount of plot points, but while one plot point may need three scenes to properly set up its full impact, another plot point may need only one scene because the natural timing of such a moment would take as long to setup as those three scenes.
Many stories have a blatant downfall that they are seemingly unaware of: nothing happens for a long period of time, because they believe their structure carries the film. The idea of structure is that these moments are all perfectly placed so that the audience can’t go too long without getting bored, and so the story remains clear because the moments are all evenly spaced. However, all of these moments mean nothing if they don’t have the intended impact, so this is where story beats are treated like the rhythm of the story. Pacing issues are what come up not when the story structure Key Moments aren’t precisely where they are required to be, but when scenes – much like music – have a disorganized sequence of beats and thus it is not enjoyable to sit through. One scene can have 10 beats and so a lot happens, then the next scene only has 2, but if a key moment is something that is a surprise then it may require many beats to distract and keep the audience on their toes; if the Key Moment is meant to be a fast action scene, then the beats before hand may be few and far between but all in the name of creating suspense. The issue is when stories believe they are creating a certain type of emotion or moment, but they don’t do justice to how long or how many beats such a moment would naturally require.