Common Cause and Special Cause [E219]

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Comebacks. Rechecks. Catastrophic parts failures. The stuff that makes everyone’s stomach drop. Matt makes the case that a big part of management’s day-to-day job is not “policing people,” but acting like an investigator—leading with genuine curiosity to figure out what actually happened and what should change.

Using Dr. W. Edwards Deming’s framework, Matt breaks problems into two buckets:

1. Common cause: Variation that’s built into the system (processes, tools, training, information flow, software, vendors, documentation, workflow chaos, etc.). These problems are repeatable—and if you don’t change the system, they’ll happen again.
2. Special cause: A true one-off—rare, hard to predict, not systemic. Sometimes the correct response is support, not a giant policy overhaul.

The goal: build trust, reduce fear, and improve the shop over time through “constancy of purpose”—not knee-jerk blame.

Key Talking Points & Takeaways

1) Management’s role when things go wrong

1. Be an investigator, not a prosecutor.
2. Start with: What happened? Why did it happen? What made it easier to fail than succeed?

2) Deming’s lens: common cause vs. special cause

1. Most problems are common-cause (system-driven), not “someone screwed up.”
2. Mislabeling causes creates chaos:
3. Treating common-cause problems like special-cause ones = scapegoating, fear, repeated failures.
4. Treating special-cause problems like common-cause ones = overcorrecting, unnecessary rules, wasted effort.

3) Examples of common-cause “system” failures (shop edition)

1. Torque wrench out of calibration.
2. Scan tool software out of date / tooling gaps.
3. No real shop management system (handwritten tickets, misreads, manual re-entry).
4. Process interruptions / constant context switching.
5. Cheap unknown parts sources creating avoidable risk.
6. Lack of SOPs, training, or accessible info.

4) What a real special-cause looks like

1. A normally reliable part fails unexpectedly (the one “bad water pump” out of hundreds).
2. A rare freak mistake by a trusted specialist with no obvious systemic trigger.
3. Response: support the person, document it, monitor trends—don’t build policy off a unicorn.

5) The trust factor

1. When leadership doesn’t jump straight to blame, the team feels safer.
2. Psychological safety improves communication, honesty, and long-term quality.

Practical “Investigator” Questions for Comebacks/Rechecks

1. What changed (tools, parts source, workflow, staffing, interruptions, information)?
2. Was the process followed—and if not, why was it hard to follow?
3. Was the right info available at the right time?
4. Was the equipment accurate and current?
5. Is this repeatable (system) or truly rare (special cause)?
6. What system change makes the “right way” easier and the mistake harder?

Mentioned / Referenced

1. Dr. W. Edwards Deming
2. Common cause vs. special cause variation
3. Deming’s 14 Points
4. “Constancy of purpose”
5. Social media’s tendency to supercharge blame and hot takes

Listener Call-to-Action

Matt wants your thoughts and stories:

1. Have you seen a shop handle a comeback well?
2. What system fixes reduced repeat issues?
3. Where does blame creep in—and how do you fight it?

Contact Information

1. Email Matt: mattfanslowpodcast@gmail.com
2. Diagnosing the Aftermarket A - Z YouTube Channel
3. Subscribe & Review: Loved this episode? Leave a 5-star review on Apple Podcasts and Spotify

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