Just In Time is Never Just-Too-Little
If there is one concept in operations that is consistently misunderstood, it is Just-in-Time (JIT).
For many organisations, JIT has been reduced to a slogan: strip out inventory. For others, it goes further and condemns Lean, a fully thought-through operating system.
These interpretations miss the point entirely.
To understand the point of JIT, it’s worth taking a trip down memory lane to the 1950s when Taiichi Ohno, the architect of the Toyota Operating System, and some of his merry men visited Ford in Dearborn. It wasn’t the factory tour that crystallised the concept of JIT, it was a visit to the supermarket.
Ohno noticed that supermarket shelves were only replenished when customers removed items, and only in the quantities actually taken.
Stock moved because of pull, not push. A carton of milk was taken from the shelf (customer pulls) and the empty shelf triggers a replenishment that cascades back through the value chain.
For Toyota the same application meant pulling from a reduced holding of parts on the assembly line workstation. The consumption of parts triggers a production signal for the upstream processes using a kanban signal.
If we follow the supermarket story, the idea was to never run out of stock on the shelf, as we want customers to buy at their convenience. It was about stocking to demand, utilising the most costly footprint effectively by holding a minimal amount (that of the shop) and replenishing based on demand.
Kanban was the bridge that carried the supermarket idea into Toyota’s burgeoning operating system.
JIT was never solely about removing inventory for the sake of it. It is about synchronising production with the rhythm of customer demand, and building a system that can supply the right product, at the right time, in the right quantity. And in the assembly area, being able to deal with optionality, customer choice, as the footprint can now cope with multiple variants.
In other words, JIT is not a reduction strategy in isolation. It just so happens that with PUSH systems we see over-production and the paradoxical situation of having a lot of WIP that we don’t necessarily need and an acute shortage of the stuff we do need – urgently. In this environment, stopping over-production with the introduction of a pull system makes logical sense, and at this point, an assessment can be made as to how much WIP is needed to protect the system. And yes, in most cases, we find that value streams could do with some inventory reduction.
So JIT, in a healthy value stream, is more of a synchronisation philosophy.
The Real Purpose of JIT
Toyota developed JIT not to save cost but to achieve flow and stability.
The central question was always:
How do we create a system that runs smoothly every day?
To answer it, Toyota developed a set of interrelated practices:
Takt: pacing production to customer demand
Heijunka: levelling work to prevent surges and overburden and expose waste
Continuous Flow: reducing batching, waiting and stop-start disruptions
Kanban: replenishing based on actual consumption
Managed Buffers: not removed inventory, but intelligent inventory to maintain flow and minimise potential defects in play
This is why Toyota’s system is calm, controlled, and repeatable – even under stress.
Why JIT Is Deeper Than “Reduce Inventory”
The actual practice of JIT is inseparable from the management of the Three Ms:
MURA (Unevenness) – Causes instability and firefighting
MURI (Overburden) – Causes breakdowns, stress, and errors, exacerbated by MURA
MUDA (Waste) – The symptom of poor flow, not the cause and perpetuates MURA with over-production.
Companies that remove stock without addressing Mura and Muri simply expose Muda and create stress.
This is why many JIT ‘experiments’ fail; they focus on tools, not the conditions that enable flow, followed by the famous words: we tried that kanban rubbish and we’re not doing that again.
Why JIT Endures
Toyota has endured oil shocks, recessions, supply disruptions, currency swings, and global crises.
This resilience does not come from low inventory.
It comes from:
- Flow designed from first principles
- Decades of people development
- Deliberate balance between Just-in-Time (flow) and Jidoka (build quality in)
- A system that grows capability over time
JIT is not a tactic. It is a way of enabling us to sees, to use critical thinking, and to lead effectively.
Conclusion
Ohno’s Real Objective: Reducing Process Lead Time, Not Inventory
Taiichi Ohno was explicit when he wrote: the central aim of Toyota’s production system was reducing process lead time, not cutting inventory. Shorter lead time meant Toyota could respond faster to customers, detect problems earlier, stabilise flow, and outperform competitors in both quality and delivery. Inventory reduction was never the goal itself, whilst also being considered a waste. When lead time shrinks, excess stock reveals itself as unnecessary, and this is the moment to reduce WIP. For Ohno, the competitive strength of Toyota came from speed of flow, not dogmatic reduction linked, say, to Trade Working Capital. The faster a product moved from raw material to finished car, the more flexible and resilient the system became. In this way, JIT was a strategy for market responsiveness, not cost-cutting.
