In order to be agile, teams need to be able to complete work fast and switch to the next area of focus. In the school of thought of 'Lean', this translates into having a short cycle time. Core to having a short cycle time is to minimize work in progress. The Cumulative Flow Diagram is an almost magical tool to visualize and manage work in progress, cycle time, and hence agility. Here I try to drive home the core concept of why reducing work in progress is 'good'.