I sometimes think about how we take technological progress for granted. Not only can it stagnate, in some cases it can even be lost. My favourite example is that the ending of the 1998 movie The Parent Trap would not be possible today:
Both realize they still have feelings for one another, but decide it is better to go their separate ways. Elizabeth and Annie later board a flight for London, but when they arrive, they find Nick and Hallie waiting for them (having taken a faster flight on the Concorde). Nick realizes his previous mistake of not going after Elizabeth…
Less immediate to everyday life, the Space Shuttle is no longer operational; reusable space vehicles are a thing of the past. I saw on TV both the landing of the last Concorde flight in 2003 and the last Space Shuttle landing, of Atlantis, in 2011.
Yet another curious example is that of low-background steel. in short, some medical apparatus and instruments like Geiger counters need to be able to detect minute quantities of radiation. But since the decades of atmospheric nuclear tests in the 40s, 50s and 60s, it is no longer possible to produce steel that is not contaminated with what are called radionuclides. The only way humanity can now make such instruments is by repurposing steel from sunk world war 2 warships.
This thread has several examples of technological regress in the past. While our world today deals mostly with the problems of too much technology-driven disruption, it’s worth being aware of how knowledge and capabilities can also be lost.