For thirty years manufacturers competed to hold less .
Parts arrived days, sometimes hours, before they were needed.
The savings were real: are expensive and ties up cash.
The weakness only appeared when several shocks arrived together.
A single factory closure could stop an assembly line on another continent.
Firms discovered they did not know their beyond the first tier.
Many are now mapping the chain two or three levels deeper.
Some hold a of critical parts again, accepting the cost.
Others split orders between in different regions.
Both choices reduce in normal times, which is exactly the point.
Shareholders, however, judge managers on quarterly results.
A manager who pays for looks wasteful until the year it is needed.
That is why memories of disruption fade faster than the risk does.