Communicate the Design

You've done the engineering. The system works on paper and it's safe for the people around it. None of that matters yet, because nobody builds a system that lives in your head. The proposal is the bridge between the engineering and the customer's decision, and it's engineering too, not a sales pitch. Its whole job is to give the customer enough accurate information to make a real decision, including the things the system can't do. So this is where the drawing becomes the plan every trade builds from, where the numbers become a business case the money can approve, and where the whole design becomes one honest document you can carry into a room and defend. A technically perfect system that you can't communicate loses every time to a lesser one that's clearly explained. Communicate it well and it gets built. Communicate it poorly and it dies in a meeting.