Keep one completed output in reserve after the constraint — a stock buffer for variability
Maintain one completed output in reserve after your constraint step (stock buffer) to decouple production cadence from delivery cadence when the constraint step has high variability.
Why This Is a Rule
When your constraint step has high variability — sometimes it takes 2 hours, sometimes 8 — downstream delivery becomes unpredictable. Stakeholders experience either feast (everything arrives at once when the constraint clears) or famine (nothing arrives during constraint delays). This unpredictability erodes trust and creates pressure to rush the constraint, which further degrades quality.
A stock buffer — one completed output unit sitting in reserve between the constraint and delivery — decouples production cadence from delivery cadence. When the constraint has a slow day, the reserve unit ships. When the constraint has a fast day, it replenishes the reserve. Delivery stays steady regardless of constraint variability.
This is the same principle behind inventory buffers in manufacturing and content buffers in publishing ("always have one article in the bank"). The buffer absorbs variability at the constraint without transmitting it downstream.
When This Fires
- Your constraint step has high output variability (some days productive, some days not)
- Downstream consumers or stakeholders complain about inconsistent delivery
- You're under pressure to "ship something" during a constraint's slow period
- Any workflow where constraint variability creates visible delivery inconsistency
Common Failure Mode
Consuming the buffer and not replenishing it. The reserve unit ships during a constraint delay, giving you breathing room — then the next fast constraint day's output ships directly instead of restoring the buffer. Now you're back to zero reserve and the next slow day has no cushion. Discipline: fast constraint days replenish the buffer first, then ship additional output.
The Protocol
(1) Identify your constraint step and its typical output unit (a blog post, a code review batch, a design deliverable). (2) Build the buffer: produce one extra output unit before delivery begins. (3) Maintain the buffer: when the constraint has a fast day, replenish the reserve before shipping surplus. When the constraint has a slow day, ship from the reserve. (4) Monitor buffer level: if the reserve is consumed more often than replenished, the constraint's capacity needs attention.