To reduce WIP and improve flow is to decrease the batch sizes of the work—the requirements, designs, code, tests, and other work items that move through the system. Small batches go through the system more quickly and with less variability, which fosters faster learning. The reason for the faster speed is obvious. The reduced variability results from the smaller number of items in the batch. Since each item has some variability, the accumulation of a large number of items has more variability.