The Problem with the “Wedge” Metaphor in Lean Standardized Work

TL;DR: The wedge metaphor, often used to represent standardized work in Lean, can send the wrong message. Instead of assuming people will backslide without enforcement, we should focus on engaging them in meaningful improvements they want to sustain. Maybe it's time to retire the wedge–and the mindset behind it.

How Standardized Work and Kaizen Are Commonly Explained

There are variations of graphics out there that are meant to illustrate how Standardized Work and Kaizen fit together. Kaizen is often articulated or illustrated in terms of “Plan Do Check Act” (PDCA) or “Plan Do Study Adjust” (PDSA) or whatever variation.

Before getting to the images (or “visuals” as some call them), let's talk about this more in concept — and maybe that will illustrate how illustrations are needed or helpful?

The Assumption of Forward Progress in Continuous Improvement

The one notion is that Kaizen means progress… moving forward and bettering our performance. We might think of that as going up.

Then, many say that there's a natural risk of backsliding… performance drops, maybe that's because people go back to their old ways.

What the Backsliding Argument Misses: Engagement and Ownership

I think there are important questions of engagement and change management that often go unillustrated. If a Kaizen-based improvement is truly a “change for the better,” why would people go back to their old ways? Maybe they go back because they aren't committed to the changes or the new way, and maybe the root of that is a lack of involvement and engagement.

I don't know if “laws of entropy” really apply in the workplace. Blaming physical chemistry (and “laws”) seems to deflect attention (or blame) from our role as leaders or change agents.

Standardized Work Should Enable People — Not Control Them

I believe strongly that if we properly engage people in creating changes that are truly for the better, then backsliding is NOT inevitable.

Do we need to keep improving? Of course.

How the ‘Wedge' Metaphor Emerged in Lean Thinking

So, if you believe that backsliding is natural and inevitable (or if you blame workers for not buying into your change), then “standardized work” is often suggested as the way to “lock in” changes — to prevent backsliding.

I believe very strongly that Lean is not about forcing people to follow procedures and standardized work. We have to make sure that it's the right standardized work and that it's easy to do things the right way.

The Popular Visual Metaphors Behind Standardized Work

So, anyway, on to the graphics.

We usually see some sort of disc or sphere that we're trying to get up a hill. These are usually two-dimensional drawings, but there's something round-ish that we need to get uphill.

The Rock, the Hill, and the Origins of the Wedge Image

When I say “round-ish” there is a Lean Enterprise Institute graphic that shows a rock. It looks like a John Shook graphic that might have origins from Toyota:

Maybe surprisingly, that image looks like a safety and ergonomics nightmare — an injury waiting to happen! A tiny wedge like that wouldn't hold a boulder at all!

Why the Wedge Became the Stand-In for Standardized Work

We can't have that (and LEI and Toyota wouldn't want injuries), so people started illustrating standardized work as a “wedge” that locks in improvements. Sometimes, the wedge is labeled as something like “Lean Management System” (it's a versatile illustration, apparently).

The wedge is whatever you want it to be?

The wedge does the work formerly done by a person… it seems safer (or it's supposed to be). It might be drawn like the image below (and the circle might be split into four equal quadrants of PDSA).

The wedge is probably poorly designed if a person has to hold it up, but I've seen it drawn that way. More on this later in the post.

Testing the Wedge Metaphor Against Reality (and Physics)

What does AI think that would look like in real life?

It doesn't look like that would work. I wouldn't trust that orange wedge. Safety first? We'd need something better.

Google Gemini adds:

Based on physics principles, the current flat-faced wedge shown in the image is not the most effective shape for preventing the blue ball from backsliding. A more effective shape would be one that conforms to the curvature of the ball.

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Why Mike Rother Argues It's Time to Retire the Wedge

Mike Rother has asked if it's “time to retire the wedge?,” as Mark Rosenthal blogged about here.

See Mike's slides about this via SlideShare:

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Mike says, in a slide, that Toyota wouldn't blame a worker for some appearance of backsliding, which I appreciate. Instead of not “slipping back,” we should continue moving forward. Let's not keep things static… I agree!

When the Physics of the Metaphor Completely Break Down

Back to wedges… I've seen some that are drawn like this:

I don't understand the physics of that one at all. Is that wedge really wedged into the ramp or the mountain that the boulder is sitting on? That stick figure looks a bit concerned, perhaps. Maybe he has a hammer to really pound in that wedge.

That looks perilous!

Maybe I'm obsessing over the wrong thing… but if we're going to use illustrations, we should make sure the physics are sound.

Some wedges are drawn like this:

Maybe that wedge from the previous drawing has fallen… what's holding up that round rock?

This seems like an “Oh No, Lean Leaper!” moment, ala Mr. Bill. The drawing is NOT the LEI “Lean Leaper,” which is a trademarked character. This is just his — or her — cousin.

This is why we don't want backsliding. That is dangerous too!

And then we would get this:

I should stop with the AI versions…

Our standardized work metaphor has gotten really grim.

Some illustrations look like the one below… which might seem like less of a death trap:

I'm an engineer, so I'm bound to think about “failure modes” — what about a strong breeze? How low is the coefficient of friction on our wedge?

We know how that story ends (unless the boulder flies over Mr. Lean Leaper).

What the Wedge Metaphor Ultimately Gets Wrong

So, here's the moral to the Lean story:

Backsliding might not hurt us if we duck?

Maybe the wedge needs to have a better shape:

Again, from Google Gemini… Here's why a different shape would be better:

• Increased Contact Area: The current flat wedge only touches the round ball at a single, small point. A wedge with a concave or curved face that matches the ball's surface would create a much larger area of contact.
• Better Grip and Force Distribution: This increased contact area would distribute the force more evenly and provide a better grip on the ball. This “cradling” effect would significantly increase the friction and resistance, making it much harder for the ball to roll over or slip past the wedge.

Gemini thinks it should look like this:

Or this:

I'm with Mike Rother; instead of getting the right wedge, let's retire the wedge… and not just because of the physics involved.

A Better Metaphor — And a Better Mindset

Maybe it's not about finding the right wedge shape after all. The real goal isn't to lock in improvement like we're afraid of backsliding–it's to create conditions where people want to sustain and evolve the change because it works better for them and their customers.

Instead of obsessing over holding the rock in place, maybe we should shift our focus to creating momentum. What if the rock isn't being pushed up a hill, but is rolling forward on a smoother, continuous path–powered by engaged people and a shared purpose?

Let's stop relying on metaphors that assume resistance or failure. Let's design systems, visuals, and leadership approaches that reflect trust, understanding, and the power of participation.

As I explore in my book Healthcare Kaizen, when people feel safe and supported, they don't need to be forced to maintain improvements–they'll drive the next ones.

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If you’re working to build a culture where people feel safe to speak up, solve problems, and improve every day, I’d be glad to help. Let’s talk about how to strengthen Psychological Safety and Continuous Improvement in your organization.