Experts may be able to articulate the vision earlier, though even experts often have to write to discover what they want to say. In the course of this sharpening, you may also find places where you need to say more, holes in the argument, jumps that are too great for a reader to make. Newton benefited from criticisms by others in this process, though he often resented them. This final polishing is extremely important. We live in a world of appearances where scratches, bugs or glitches are used to condemn an otherwise powerful new vision.
Revision takes time.
You have to live with a piece of writing, wrestle with these stages iteratively, discovering and sharpening your focus. Begin writing early, while you are still doing research. Don't worry if the first crack isn't that great. These early words are taking you towards your goal. A great deal of scientific and technical writing is done in groups or teams.