Heuristic
Treat growing WIP as a delay signal
Accumulating work usually means elapsed time will not stay neutral.
When it fits
- When more work is being started than finished and people respond by opening even more tasks.
When to avoid it
- Queueing equations have specific assumptions. Use them for directional reasoning and measurement design, not as exact forecasts for arbitrary multi-stage knowledge work.
Why it matters
If throughput is stable while WIP rises, expect average time in system to rise over a stable long-run boundary. Investigate why starts exceed completions.
An example
Five projects start each week while three finish; active work climbs and stakeholders experience longer waits despite high activity.
Check your result
The team reacts to sustained WIP growth as a flow problem rather than celebrating utilization.
Keep this limit in mind
- Queueing equations have specific assumptions. Use them for directional reasoning and measurement design, not as exact forecasts for arbitrary multi-stage knowledge work.
Connected ideas
Useful withLimit parallel starts when completion is the goal
Evidence and sources
Supports
Little's Law relates long-run average work in a stable system to arrival/throughput rate and average time in system as L = λW under stated mathematical conditions.
The relation does not identify root cause, queue discipline or the correct intervention; workplace applications must respect the assumptions.
A Proof for the Queuing Formula: L = λW · Abstract