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.