I have made the mistake of cramming so much backstory and unnecessary description into my early drafts that bogged the reading down and made the story almost incomprehensible. I had so much in my head I thought I needed to convey. It has taken years for me to pick out just what information the reader needs to know from the breadth of story details in my head. And even then I usually add more that gets cut in later drafts. But the advice to narrow my scope allowed me to focus on character motivation and POV, and those were my roads into a deeper story.