The main objective of a "pull-driven" approach is to produce
finished products as optimally as possible in terms of quality,
time, and cost, so as to satisfy customer demand. Achieving
high process throughput while minimizing operating expenses
including in-process inventories is key. Keeping busy by
processing just any one of the resources in the input queue of an
activity requiring a combination of resources is insufficient. To
pull means that resources must be selectively drawn from
queues— so the activity that processes them will be busy just the
same— but chosen so that the activity's output is a product
needed further downstream in the process, and needed more so
than its output using other resources in the queue would have
been. Resources' wait time in queues should be minimized.