Chapter 11Managing Work in Progress
In any kind of workflow it is useful to distinguish work states and wait states. When the mail carrier is carrying an envelope to your mailbox, that envelope is in a work state (because something is happening to it). When it is in your mailbox, the envelope is in a wait state (because nothing is happening to it).
The reason we need mailboxes is because you aren’t always there to receive an envelope when the mail carrier arrives. Your mailbox is a buffer—a place for things to hang around in while waiting for the next step in the process.
Now if you study the project board closely, you’ll see that only four of the columns represent work in progress (WIP). The other six columns are buffers (or queues), highlighted ...