It's not that simple, though. "What if our supply chain of X is disrupted?" always leads to a problem where one of the most obvious solutions is "Stockpile huge inventories of X!"

That's what manufacturers had done ever since Ford tried to scale up his initial (very Toyota-esque) operation, and scaled it incorrectly but managed to inspire hordes of other manufacturers to repeat his mistakes.

The novelty of Toyota et al. was not that they asked the what if question, but that they answered it unconventionally: they worked on making the supply chains more reliable instead of adding buffers.

That's what makes this next move counter-intuitive to so many people: when Toyota encountered a supply chain that couldn't be made more reliable, they chose the previously-conventional response, apparently in defiance of their whole thing. Except it wasn't.

You're right in that it is simple, but in trying to show that you're making it too simple.

I think that is the easy way to answer that question. Obviously the first "What if .." should be try to source from somewhere else, or perhaps have multiple supply chains. For instance cloth is a commodity, and if they know they can get the quality they need from multiple vendors on all 7 continents - they don't need to do much except perhaps validate the supply chain of some selected to ensure they don't source from the same place. But if they are using a particular mineral that is only available from one location, something else must obviously be done.

Just stockpiling is not really an answer as much as it's trying to just do the least amount of problem solving and thinking.