Heuristic
Move quality checks upstream of the bottleneck
Do not spend the constraint on defects that cheaper checks can catch.
When it fits
- When scarce capacity repeatedly rejects preventable bad inputs.
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
Add lightweight validation before the bottleneck for recurring failure modes, while retaining the bottleneck's judgment on risks only it can assess.
An example
Before specialist review, an automated schema check catches missing fields so expert time goes to semantic exceptions.
Check your result
The constraint receives fewer preventable defects without merely moving hidden error downstream.
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 withSeparate touch time from queue time
Evidence and sources
Provides context
Kingman's heavy-traffic result underlies a queueing approximation in which waiting increases sharply with utilization and with variability in arrivals and service.
It is a single-server heavy-traffic approximation and should be used as directional intuition, not as an exact prediction for arbitrary multi-stage work.
The Single Server Queue in Heavy Traffic · Research note metadata and established heavy-traffic formulation