"If it is any use to know it, I always try to write on the principle of the iceberg. There is seven-eighths of it underwater for every part that shows. Anything you know you can eliminate and it only strengthens your iceberg. It is the part that doesn’t show. If a writer omits something because he does not know it then there is a hole in the story." - Ernest Hemingway
I think this is useful at two points.
First, it underscores the importance of getting to know our characters, including many things we will not end up including in the script or manuscript.
Second, when revising the first draft cut the bits where you've pictured the entire iceberg for the reader. Leave the one-eighth that allows the reader to know or at least sense the other seven-eighths.
