Starting and building
Taiichi Ohno
Ask why five times
Taiichi Ohno (1912–1990 · Toyota, Japan) — Ask why five times.
What actually happened?
The book came out in 1978 and the world copied the visible half. Factories everywhere put up the boards, printed the cards, hung the cords, learned the vocabulary, and left their buffer stocks exactly where they were. The cord was there and nobody pulled it. What had been copied was the equipment; what had not was the point of it, which is that the whole system is an instrument for making problems impossible to cover up. Remove the willingness to be embarrassed in public, at the moment it happens, and none of the hardware does anything.
The first cause is almost never the cause
A machine stops. The fuse blew — but why the overload? The bearing was not lubricated. Why not? The pump was not pumping. Why not? The shaft was worn. Why? No strainer was fitted and metal scrap got in. The fifth answer is the repair, and it is the cheapest thing in the chain.
He was careless this time is a fuse. Keep going: why was he careless, and what made being careful impossible there?
The power to stop belongs at the bottom
Whoever sees a problem first is on the line, not in the office. If only a manager may stop, the fault has to travel upward and wait for permission, and by then it has flowed past. An error caught at the first station costs a minute; found at the last it costs the whole unit.
Letting the person doing the work say wait, this is not right is worth ten times any inspection afterwards.
Inventory is water and problems are rocks
With the water high the boat runs smoothly, because every rock is submerged: the unreliable machine, the supplier who misses dates, the handover nobody sorted out. Lower the water and they surface one at a time. Every margin is underwriting some problem, and an underwritten problem never gets repaired.
Whichever stage always keeps a margin has, underneath that margin, a problem nobody has fixed.
Stopping is what produces
Management's instinct is to keep the line moving, because output matters. What keeps moving, though, is defective output, and more of it is worse. He inverted the order: you stop in order to produce, and refusing to stop is what actually cuts production.
Get it out now and fix it later mostly produces rework, and rework costs far more than the pause would have.
How do I use it today?
Take one problem that has come back three times. Write the incident at the top of a page, then ask why underneath it five times, each answer becoming the next question. Stop when you cannot answer. If the change implied at the bottom is small and cheap, you have reached it. If it is large, you have not.
Deep read
Read alongside
Further
Lines to keep
The man who replaces the fuse will be back next week.
When the water is high, all the rocks are underneath it.