Lean Six Sigma Principles: What the Training Slides Don’t Tell You

Lean six sigma principles are one of those things that look straightforward on a training slide and turn out to be genuinely hard in practice. The principles themselves — define value from the customer’s perspective, map the value stream, create flow, establish pull, pursue perfection — are not complicated to understand. What’s complicated is applying them in organizations that were built around assumptions that run directly against them. Most Western companies optimize for departmental efficiency. Lean six sigma principles optimize for end-to-end flow. Those two goals are frequently in conflict, and the conflict rarely gets resolved in Lean’s favor.

What is Lean Six Sigma?

Lean Six Sigma is a technique that combines the methods of Lean and Six Sigma to eliminate the eight kinds of waste in order to improve performance. The purpose of Lean Six Sigma is to improve the quality and the efficiency of the process considering customer requirements. The Lean vs Six Sigma distinction is covered in detail later — the short version is that Lean targets waste, Six Sigma targets variation, and most real problems need both.

The Five Lean Six Sigma Principles

Most descriptions of Lean Six Sigma principles trace back to James Womack and Daniel Jones, whose 1996 book Lean Thinking distilled the Toyota Production System into five principles that could be applied outside automotive manufacturing. These five principles are still the clearest framework for understanding what LSS is trying to do:

1. Define value from the customer’s perspective. Value is what the customer is willing to pay for. Anything the process does that doesn’t contribute to something the customer values is, by definition, waste. The difficulty: internal processes are usually designed from the organization’s perspective, not the customer’s. What’s convenient for the organization to produce often differs from what the customer actually wants.

2. Map the value stream. Once you know what the customer values, map every step in the process from raw material or request to finished deliverable. Identify which steps add value, which don’t, and which are necessary even though they don’t add direct value (regulatory requirements, for example). This is typically done through value stream mapping — a visual tool that shows material flow, information flow, and the time each step takes.

3. Create flow. After removing waste, the goal is to make the remaining value-adding steps flow continuously — no batching, no waiting, no queuing. This is the principle that creates the most organizational friction. Departments like batching because it’s efficient for them. Lean says batch processing is waste because it introduces delays and inventory buildup. The conflict between departmental efficiency and process flow is at the heart of most failed Lean implementations.

4. Establish pull. In a pull system, work is triggered by actual customer demand — you produce when a customer orders, not in anticipation of future orders. The opposite is a push system, where you produce based on forecasts and accumulate inventory hoping demand materializes. Pull reduces inventory waste and overproduction, but requires much more coordination and discipline than push systems.

5. Pursue perfection. The fifth principle is the one that distinguishes genuine Lean Six Sigma implementations from one-off improvement projects. Lean is continuous — the goal is to keep identifying and eliminating waste as processes evolve, not to declare the work done after one improvement cycle. This requires a culture of ongoing improvement, which is the hardest principle to sustain and the one most organizations quietly abandon after the first year.

What is Lean?

Lean is a problem-solving tool for eliminating wastes and removing wasteful activities that don’t add value to the process. By using this tool, only the activities which add value to the process can be considered. Activities can be categorized by their values in the process. Lean focuses on maximizing customer value by using fewer resources.

Lean is not limited to manufacturing — it applies equally to service operations, healthcare, financial processes, and knowledge work. The confusion comes from its Toyota factory origins, which makes it easy to assume the tools only apply to assembly lines. The principles — identifying value, mapping flow, eliminating waste — work anywhere work moves through steps.

The origins of Lean are specifically Toyota. Taiichi Ohno, chief engineer at Toyota, developed the Toyota Production System in the 1950s and 60s as a response to the constraints Toyota faced after World War II — limited capital, limited space, the need to produce a wide variety of vehicles in small quantities. The waste-elimination principles he developed were not originally called “Lean.” That term came from Womack, Jones, and Roos’s 1990 book The Machine That Changed the World, which studied Toyota’s methods and gave them a name that Western manufacturers could adopt.

One thing worth knowing about the Toyota origins: the principles worked at Toyota in a specific cultural and operational context. Toyota’s improvement culture took decades to build. Companies that adopt Lean tools without the underlying culture — the expectation that every employee is responsible for identifying waste, the willingness to stop production to fix a problem rather than pushing defects downstream — tend to get superficial results. The tools are necessary but not sufficient.

Value Added vs Non Value Added Activities

Value is something that a customer is willing to pay for.

Non-Value Added Activity

Non Value Added Activities do not add any value to the process. They consume time and resources without contributing to anything the customer cares about. In most organizations, non-value-added activities make up the majority of process time — estimates from Lean practitioners typically put the figure at 60-95% of total cycle time depending on the process.

Value-Added Activity

Value-Added Activities add value to the process — they transform inputs in ways that the customer values and is willing to pay for.

Value Enabling Activities

Value Enabling Activities are activities that do not add value directly to a process, but must be performed to allow Value-Adding Activities later on. Regulatory compliance, quality inspections, and some administrative steps fall into this category.

The categorization sounds clean in theory. In practice, there’s a lot of gray area — particularly around value-enabling activities. I’ve sat in workshops where teams spent forty minutes debating whether a particular approval step was “value-enabling” or “non-value-added.” The answer was non-value-added. The debate itself was also non-value-added. The test is simple and uncomfortable: if you eliminated this step, would the customer notice or would a regulatory requirement go unmet? If neither, it’s waste. Most organizations have a lot more of it than they want to admit, which is why the categorization exercise tends to slow down and get political.

What Are the Eight Kinds of Waste?

Waste can be anything except the materials and resources that add value to an activity. Therefore excess materials, overproduction, idle time, and unnecessary motion are all forms of waste. The eight wastes are commonly remembered using the acronym DOWNTIME:

• Defects — products or services that fail to meet requirements, requiring rework or scrapping
• Overproduction — producing more than the customer currently needs
• Waiting — idle time between process steps
• Non-utilized talent — unused skills, knowledge, and creativity of employees
• Transportation — unnecessary movement of materials or information
• Inventory — excess stock that isn’t immediately needed
• Motion — unnecessary movement of people
• Excess processing — doing more work than the customer requires

The eight waste was the one added latest — non-utilized talent wasn’t in Ohno’s original seven. It was added as Lean spread into service and knowledge work environments where the most significant waste is often in how people’s capabilities are deployed, not in material flow. In knowledge work organizations, non-utilized talent is frequently the largest single waste: qualified people spending most of their time on administrative tasks, approval processes, or rework caused by upstream process failures.

Worth noting: the DOWNTIME acronym is the more common version in Lean Six Sigma training. The older version — TIMWOOD or TIMWOODS — covers the same wastes in a different order. Both refer to the same framework. If you’re in an organization that uses one and you encounter the other, it’s the same list. Don’t let the acronym become the thing you remember instead of what the acronym stands for. I’ve met Green Belts who could recite DOWNTIME perfectly and couldn’t identify a single waste in the process they were supposed to be improving.

What Are the Benefits of Using Lean Six Sigma Principles?

Organizations that implement Lean Six Sigma principles consistently — not just as a one-off project but as an ongoing operational approach — see measurable improvements across several dimensions:

• Cost reduction through elimination of waste and rework
• Faster cycle times through flow improvement and elimination of waiting
• Higher quality through defect reduction and variation control
• Better use of people through attention to the non-utilized talent waste
• Customer satisfaction through delivery of what customers actually value

These benefits are real and documented across industries — manufacturing, healthcare, financial services, logistics. The caveat is that the benefits are proportional to how deeply the lean six sigma principles are embedded in how the organization actually operates, not just in project-level initiatives. Organizations that run LSS projects without changing the underlying management system tend to see improvements that don’t persist. See our article on six sigma in project management for a more detailed look at where these benefits appear — and where they don’t.

What Are the Differences Between Lean Six Sigma and Six Sigma?

Lean targets waste — non-value-added steps, waiting, overproduction, unnecessary motion. Six Sigma targets variation — the inconsistency that causes defects and unreliable output. They were developed separately and combined because the problems they solve usually coexist. The tools overlap significantly: control charts, fishbone diagrams, and Pareto analysis appear in both. The DMAIC framework (Define, Measure, Analyze, Improve, Control) is specifically Six Sigma; value stream mapping and 5S are specifically Lean. Most real improvement initiatives pull from both sets.

The practical question is where to start. If cycle times and wait times are the primary problem, start with Lean waste identification and value stream mapping. If defects and process inconsistency are the primary problem, start with DMAIC and Six Sigma measurement tools. In most organizations it’s both, which is why the combined methodology exists. See the Six Sigma methodology article for a deeper look at the Six Sigma side.

	Lean	Six Sigma	Lean Six Sigma
Primary goal	Eliminate waste	Reduce variation	Both
Key question	Which steps add value?	Why is output inconsistent?	Both questions at once
Framework	Value stream mapping, 5S, kanban	DMAIC	DMAIC + Lean tools
Origin	Toyota, 1950s	Motorola, 1986	Combined 1990s onward
Use when	Process is slow or wasteful	Output is defect-prone	Both problems present

Why Lean Six Sigma Principles Are Hard to Sustain

A few years ago I ran a 5S implementation in a distribution warehouse — about 80 people, three shifts, chronic problems with inventory location errors and time wasted searching for stock. Pick error rate was running around 11% at baseline; shift supervisors estimated they were losing 20-25 minutes per handover to locating misplaced items. We spent six weeks mapping, running workshops, relabeling, building shadow boards, establishing visual controls. By the end of month one, pick errors were down to around 3% and handover time had dropped to under 10 minutes. Numbers the operations director was happy to show the MD.

By month four, the shadow boards had items missing. Two sections had reverted to free-form storage because a new team leader joined and hadn’t been briefed. Pick errors were back up to around 7% — not the original 11%, but nowhere near 3%. When I raised it with the operations manager, he said: “We just got busy.” No budget for sustaining the system. No weekly 5S audit in the schedule. No named zone owners. The improvement had an end date. The process didn’t.

That’s the fifth lean six sigma principle failing in real time — not because it’s wrong, but because no one built the management system around it. The tools worked perfectly. The results were real. What wasn’t there was the ongoing management discipline to treat the new standard as the standard, not as a project output that could be deprioritized when things got hectic.

The lean six sigma principles themselves are sound. The organizational conditions required to sustain them are more demanding than most training programs acknowledge. That gap is probably worth understanding before you start — not to be discouraged by it, but to scope the commitment realistically.

In your organization, when someone says “we’re doing Lean” or “we ran a Kaizen event” — is it a genuine management system or a project that ran for three months and got filed? I’m genuinely curious whether the fifth principle — pursue perfection — is something anyone actually treats as ongoing or whether it’s more of a closing slide on the training deck.