The article discusses the importance of writing good design documents, which are technical reports that outline the implementation strategy of a system. A good design document should convince the reader that the design is optimal given the situation, and the most important person to convince is the author themselves. The article provides tips on how to write a good design document, including organizing the document well, editing for length, and using an appendix for complex calculations. The goal of a design document is to take the reader's mind from their current state to a new state where they believe the design is a good one.