mekka okereke 
Martin SeegerWhat a lot of people do not understand is the fragility of supply chains.
Setup
Let us assume there is a part X that is used by a large number of other companies. It is not glamorous, it is not expensive, and nobody outside a small circle of specialists ever thinks about it. But it is needed. Without it, other products cannot be finished.
Everything is fine
Part X is made by a small company with a few dozen employees and a machine that is several decades old.
Everything runs smoothly. The company knows how to maintain the machine. They know how to operate it. They know its strange noises, its moods, its undocumented rituals. They know which lever needs a bit of persuasion on cold mornings and which replacement part must be machined by hand because nobody has made the original since 1987. They also know how to train new employees, because the knowledge still exists inside the company.
Crisis
Then, suddenly, a few large customers run into a crisis.
Orders slow down. The warehouses fill up with part X. Prices fall.
The company downsizes. Then it downsizes again. But nobody really notices, because stocks are still full. Customers are not yet affected. Purchasing departments can still get part X from inventory. Balance sheets still look fine. The problem has not yet reached the spreadsheet.
If this goes on for long enough, the company goes broke.
Again, nobody really notices. Stocks are still full. Some people may worry, but as long as no current production line is stopping and no quarterly number is visibly bleeding, nothing urgent is done.
The employees move on. They retire, change industries, start new careers. The old machine is sold for scrap. The building is repurposed. The knowledge evaporates.
Recovery
A few years later, demand picks up again.
The warehouses slowly empty. Stocks run low. People start ordering part X again, only to discover that nobody is offering it anymore.
Now someone decides to restart production.
The first thing they discover is that there is no machine. Building a new one would be prohibitively expensive, assuming anyone still knows how to build it properly. So they desperately search for an old one.
They get lucky. In a scrapyard, they find a machine that used to produce part X. It is rusted, incomplete, and dysfunctional. Naturally, they buy it.
Now they try to get it working again.
But there is another problem. There are no people left who know how to maintain it. So they hire someone who understands industrial maintenance in general, but has never worked on this specific machine. That person does their best. They improvise. They read old manuals. They reverse-engineer undocumented fixes. They keep the machine alive with skill, patience, and increasing amounts of despair.
But it breaks down every few hours. Output is abysmal.
Bottlenecks
And now that one poor maintenance person is overworked. They need help. But training help requires time, and the only person who can train others is the same person needed to keep the machine barely running. Every hour spent teaching is an hour not spent preventing the next failure.
Very few businesses survive this phase.
There is no institutional knowledge anymore. New people are hired, begin training, look at the state of the machine, the chaos of the process, and the constant emergency mode, and conclude that the business is doomed anyway. Then they quit.
Churn becomes terrible. Even if the company survives financially, it remains fragile. It is always just one or two people quitting away from disaster.
At the end the world decides it needs to get rid of part X as the supply is too fragile.
Summary
This is still very much simplified. The reality is more complex, more ugly.
And that is the part many people miss: a supply chain is not just warehouses, contracts, prices, and transport routes. It is also people, habits, obsolete machines, informal knowledge, and boring little skills that nobody values until they are gone.
Wolfie Christl
HeavenlyPossum
display name 
Hal Pomeranz
TinDrum
IXI
Heidi Li Feldman
infrastory