For an object-level example, look at the difficulties the Russians had reconstituting their industrial base in the post-apocalyptic wasteland they found themselves after the 90s. It took them a decade to figure out how to restart production of the Tu-160M bomber, and they had all the original blueprints! Likewise, for a while, we forgot how to make this "FOGBANK" substance that's somehow important for nuclear weapons.
It's all too easy to forget how to do something if you stop doing it for a while.
The main thing is to ensure you can continue to produce the machine tools, electronic components, and precision equipment needed to service each major industry. And the domestic engineering talent to run them. This allows you to add capacity quickly if self-sufficiency is needed.
Oh, and you also need to secure stable supply chains.