Toyota fixed just-in-time after 2011. It still ran dry in 2021.

In March 2011, an earthquake forced Toyota to halt large parts of its production for months. Just-in-time, the system the world copied, had shown its one failure mode.

Toyota had three options. Keep pure just-in-time. Abandon lean and stockpile everything. Or buy slack only where a missing part stops the line. It chose the third.

For roughly 500 priority parts, with semiconductors on the list, someone must always hold two to six months of inventory. That someone is the supplier, so Toyota's own plants stay lean.

In September 2011, Toyota said it was building a plan to recover within two weeks of any future disaster. When the chip shortage came, Toyota said in May 2021 that it expected no major semiconductor impact. By August 2021, it was adjusting plans again and again. In September 2021, Toyota cut about 70,000 units from September and about 330,000 from October. In January 2022, it cut about 150,000 more for February.

Toyota's full-year forecast went from 9.3 million units to 9.0 million, and then below 9 million.

Was the 2011 fix a failure? The record does not say so. It says Toyota built slack for a shock of one size, and the chip shortage ran longer than the slack. A buffer buys time. It does not make you immune.

If you run a lean operation, list the parts that can stop your line, decide who holds the stock, and write down how long a shock it covers. Then ask what you will do the month after it runs out.