In Chapter 21 of "The Goal: A Process of Ongoing Improvement," the protagonist, Alex Rogo, confronts a machinist who is causing a delay in production. The machinist explains that they are waiting on the raw materials needed to complete the job. Alex realizes that this is a symptom of a larger problem in the system and decides to investigate further. This chapter highlights the importance of identifying bottlenecks and addressing them in order to improve overall efficiency and productivity.