Breaking down a scene - Using all the tricks of the writer during a scene whether major or minor is important and deciding hoe much exposition, action, description and narration is important. Using too much of one kind may skew the scene. I've read scenes where there is nothing but dialogue. I've written them but it's important to let the reader see more than this. So looking at your scene and following the 5 Ws is important. Who, Where, When, What and Why are important for the writer to know.
The motivation for each character must be established so the reader knows exactly why a character acts the way he or she does.
So understanding motivation is important for the writer. If they don't understand the motivation of their characters expecting the reader to know and understand is impossible.