Set WIP limits based on your constraint's capacity — when the active queue is full, new items enter a backlog, not the active set
Set explicit work-in-progress limits by deciding how many active projects your constraint can handle simultaneously, and when the limit is full, new items enter a backlog rather than the active queue.
Why This Is a Rule
Set WIP limits per pipeline stage (solo: Draft=3, Review=2, Polish=2) — don't start new items until existing ones advance established WIP limits for pipeline stages; this rule extends the concept to constraint-based WIP limits across your entire project portfolio. Your binding constraint (whether it's your own attention, a key collaborator's availability, or a shared resource) has a finite simultaneous capacity. When active projects exceed this capacity, each project receives less attention than it needs, and cycle time for all projects increases (When the bottleneck is waiting, not processing — reduce work-in-progress first, because cycle time = WIP / throughput's Little's Law).
The constraint-based WIP limit makes the routing decision structural rather than ad-hoc. When the active queue reaches its limit, new items enter a backlog — a holding area for future work — rather than being added to the active set. This prevents the gradual expansion that occurs when every new request "seems small enough to take on." The backlog is not a rejection; it's a queue that feeds the active set as items complete and capacity opens.
When This Fires
- When setting up a personal project management system
- When active projects consistently exceed your capacity to advance them
- When When the bottleneck is waiting, not processing — reduce work-in-progress first, because cycle time = WIP / throughput's Little's Law analysis reveals too many items in progress
- Complements Set WIP limits per pipeline stage (solo: Draft=3, Review=2, Polish=2) — don't start new items until existing ones advance (stage-level WIP limits) with portfolio-level constraint-based limits
Common Failure Mode
Unlimited active queue: accepting every new project into the active set because "I can handle one more." Each addition individually seems manageable; collectively, the 15 active projects each receive 7% of your attention, and nothing completes.
The Protocol
(1) Identify your binding constraint: what resource limits how many projects you can advance simultaneously? Usually: your focused attention (2-3 deep projects max) or a key collaborator's availability. (2) Set the WIP limit to match the constraint's capacity: if you can meaningfully advance 3 projects simultaneously, the limit is 3. (3) When a new project arrives and the active queue is full → it enters the backlog. Acknowledge it, prioritize it within the backlog, but do not add it to active. (4) When an active project completes → pull the highest-priority backlog item into active. (5) Review the limit quarterly: if you're consistently completing active items quickly, you might increase by 1. If items stall, decrease by 1.