Unlike an auto manufacturer’s standing inventory of parts, the customers in a retail operation interact with the process even when nothing is happening. You can’t look at them like stock parts, not because it’s objectively wrong to count heads, but just because they won’t stand for it. Especially when it comes to waiting. As we discussed last week, customers flowing through a bottleneck don't just wait passively. For a retailer, an overwhelmed bottleneck is not just a cap on the overall flow rate; it can actually reduce demand.