To understand the answer in editing terms, let’s first use an analogy. Imagine a writer who authors large documents. He works on a typewriter. In order to transfer ideas from his mind onto the paper, he first threads a sheet of paper into the typewriter’s carriage. But probably not just one piece of paper. In many cases, he will insert at least two sheets with a piece of carbon paper in between. Next, he starts to type. To do this he pushes the arm on the carriage, and the entire carriage unit moves to the right. As he begins typing, the metal arms connected to each letter key pop forward and strike through the ribbon making imprints of letters of the alphabet on the paper as the carriage slowly moves back to the left. After typing one line (roughly ten words) and before every line thereafter, he must push the carriage again to the right and continue typing. If he gets every stroke right, he ends up with a sheet containing the work he set down to write. But rarely is every stroke right. More than likely, he will make mistakes and have to use white out, erasures, or some other means to cover
those mistakes. This quickly becomes a complicated matter because covering or erasing on the top sheet may be difficult enough, but doing the same to the carbon copy is virtually impossible, especially without getting ink all over one’s hands, not to mention clothing. Eventually, however, this writer will finish his first draft.