A conference paper by Soojin Jun, Miso Kim, and Joonhwan Lee that reframes system diagrams from static component arrangement toward diagrams as organizing principles that shape user action, decision-making, and shared understanding. It proposes four organizing modes—system as law (hierarchy), rule (decision-making), function (affordance/action possibility), and condition (cultural ideals)—and illustrates them through examples and a case study of the USPS Domestic Mail Manual transformation project, showing how different diagram types serve different goals across a design process.