WIP (Work in Progress) is all work that has been started but not finished: items between processes, cases under handling, orders in the system. High WIP lengthens lead time proportionally (Little’s law), ties up capital and hides problems.
WIP feels productive — everyone is busy — but every started item that is waiting is wasted calendar time and hidden risk: errors discovered late, priorities that change, switching between tasks.
WIP ceilings (as in kanban) are the simplest countermeasure: set a maximum for how much may be in progress per process, and start something new only when something is finished. Stop starting, start finishing.
The arithmetic is concrete: with 200 cases in progress and 20 closed per day, lead time is ten days — no matter how hard anyone works. To get to five days without hiring, there is only one route: halve the work in progress. That is why a WIP limit feels wrong at first and works anyway.