TOC course · Lesson 2 of 6
Identify a constraint from evidence
A queue tells you where flow stopped. Your tangible win is learning how to test what actually stopped it.
The one idea
Identify the limiting mechanism, not merely its visible symptom. Seventeen RFCs in clarification could mean too little analyst capacity. It could also mean missing customer decisions, weak intake, unclear commercial authority, oversized work batches, or a policy that lets indefinite waiting masquerade as active work.
Use four evidence lenses
| Lens | Question | Evidence to collect |
|---|---|---|
| Accumulation | Where does work wait persistently? | WIP and age by specific phase—not generic ticket status. |
| Starvation | Which downstream step lacks ready work? | Idle-ready time, ready backlog, and transitions into execution. |
| Cause | What condition prevents the next transition? | Blocked-time reason: internal decision, customer dependency, skill, commercial approval, or capacity. |
| Response | Does changing that condition increase goal throughput? | Before/after phase transitions and invoiceable output, with SLA as a guardrail. |
This follows TOC's first focusing step: identify the system constraint relative to more goal achievement. The later steps only work if this diagnosis is good enough to focus the organization rather than a local department. See the Goldratt Research Labs introduction.
Work the IT-Premium case
The updated source supplies four stronger clues:
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Accumulation: strong clue
Seventeen of 30 open RFCs were in clarification, with stale work far older than the work already executing. The specific RFC phase revealed this; the generic “in progress” status hid it.
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Capacity mix: direct evidence
June time logs show that incidents and service requests consumed well over four-fifths of logged specialist capacity. That is a system-wide execution constraint, but it does not explain why clarification RFCs are waiting for decisions.
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Touch time is not lead time
Time logs now show that clarification and execution used comparable direct effort. Phase-transition timestamps are still needed to separate elapsed lead time and wait time from touch time, and to identify customer versus internal waiting.
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Response: proposed test
Twice-weekly 45-minute decision clinics plus a protected execution block only for approved work should increase approved plans and invoiceable work without worsening SLA—if the hypothesis is right.
Do not confuse these three
| Term | Meaning | Case example |
|---|---|---|
| Queue | Work waiting at a location. | The 17 RFCs in clarification. |
| Bottleneck | A resource or step whose effective capacity is below demand in its local flow. | Could be scarce specialist discovery time—but that was not proven. |
| System constraint | The condition currently limiting more goal achievement for the chosen system. | Candidate: clarification-to-approved-plan decisions limiting invoiceable RFC flow. |
Practice: diagnose the evidence
Retrieve the missing evidence type from memory. Short phrases are enough.
The seven-day evidence card
For every RFC currently in clarification, record only:
RFC · days in phase · next decision · blocker category
blocker owner · promised date · ready for execution? yes/noAt the end of the week, count transitions to plan-ready and group blocked days by reason. The largest actionable source of lost flow becomes a stronger constraint candidate than the raw queue count.
Primary reading
- Goldratt Research Labs: Introduction to Theory of Constraints — focus on why the system constraint governs global performance and on Step 1.
- IT-Premium Value Streams & Flow Constraints — reread “Time-measurement availability,” “Measured value-stream diagnosis,” and “Four-week experiment.”