Method

Lean fundamentals

In French: Fondamentaux du Lean

Lean seeks to give the customer what they value while consuming as few resources as possible. Five principles organise the approach: define value, map the flow, make it continuous, pull it by demand, aim for perfection.

The five principles

Womack and Jones formulate them in Lean Thinking (1996) after observing Toyota. They are read in order: each makes sense only once the previous one is in place.

Define value, from the customer’s point of view. Not what the company knows how to do, not what it invoices: what the customer agrees to pay for. It is the principle most often skipped, and without it the four that follow have no sorting criterion — one then optimises activities nobody asked for.

Map the value stream. Follow the product or the file end to end, distinguishing what creates value, what creates none but remains necessary as things stand, and what is only waste. Value stream mapping is the established tool.

Make the flow run. Remove the stoppages, the batches, the waits between steps. It is the principle that most upsets organisations by function, where each department optimises its own output and pushes its work in progress on to the next.

Pull by demand. Produce only what is consumed downstream, rather than feeding according to forecasts. Kanban is the best-known mechanism of this principle.

Aim for perfection. Start the cycle again. Lean has no final state: it holds that waste reappears, and that the only sustainable answer is repeated improvement with those who do the work.

Muda, mura, muri: three forms of waste, not one

Everyday vocabulary retains muda — the task that adds nothing — and its seven families listed by Taiichi Ohno: overproduction, waiting, transport, over-processing, inventory, motion, defects. The eighth, untapped human potential, is a later Western addition.

Two other forms count as much. Mura is unevenness: a load that varies sharply from one day to the next forces the means to be oversized to absorb the peaks. Muri is the excess imposed on people or machines — the pace sustainable for a week but not for a quarter.

The three are linked, and the order of treatment matters: levelling mura often makes the muda one was about to hunt disappear, whereas hunting muda without touching mura amounts to asking the teams to absorb the unevenness — that is, to creating muri.

What Lean is not

It is not a headcount reduction plan. The shortcut is frequent because Lean does indeed reveal spare capacity; what is done with it is a management decision, not a consequence of the method. A roll-out that starts with departures no longer collects a single improvement proposed by the teams, and stops there.

Nor is it a toolbox. 5S, SMED, kanban and mapping existed separately before being brought together; what makes Lean is the order in which they are used and the definition of value that governs them.

The common mistakes

Starting with a tool because it can be taught. A 5S project is planned in a week and shown in photos; defining value with a customer requires interviews and produces a text. Yet the second governs the first — a perfectly tidy workshop that makes what nobody needs remains a workshop of waste.

Confusing the five principles with five steps to tick off once. The fifth explicitly refers back to the first: value changes when the market changes, and a map from 2024 describes a flow that no longer exists.

On the shop floor — Financial services

A file-processing department mapped its flow before touching anything: over 11 days of average lead time, 47 minutes of actual work. None of the projects considered until then — speeding up data entry, training the clerks — would have addressed the 10 days and 23 hours of waiting. The map improved nothing by itself; it avoided six months of work on the wrong problem.

The other tools illustrated by this trade: banking, insurance and back office.

Frequently asked questions

What is the difference between Lean and Six Sigma?

Lean tackles lead time and waste by acting on the flow; Six Sigma tackles variability and defects by acting on causes, through statistics. The two are commonly combined under the name Lean Six Sigma: Lean gives the speed, Six Sigma the consistency. They are not opposed, but they do not answer the same question — a fast and unstable process belongs to the second, a reliable and slow process to the first.

Does Lean apply outside industry?

Yes, and the gains there are often greater, because waiting times are rarely measured. In an administrative department, a hospital or an IT team, the "product" is a file, a patient or a request; the seven wastes carry over directly, inventory becoming the queue and transport the back-and-forth between departments.

Which principle should you start with?

With the definition of value, always. It is the only one that provides a criterion for deciding afterwards: without it, one cannot say whether an activity creates value, and therefore cannot decide what to remove. Concretely, it means interviewing real customers before gathering the internal teams.

How long before results are seen?

A targeted project — one station, one short flow — produces measurable results within a few weeks. A lasting change in the way of working is counted in years, and the limiting factor is almost never technical: it is the constancy of management in going back to the shop floor once the novelty has worn off.