For example, I grew up in the beginning of the home computer boom in the 1980's. Much of that history has completely disappeared because it was thought to be safely stored on audio cassettes and floppy discs.
Because we learnt nothing from that, the next popular storage medium, CD, lost much of the 1990's because as it turns out, they too are not indistructible.
In case you think that this is limited to home computers, today we couldn't build, let alone launch a Saturn V rocket and send it to the moon, even though we know that this happened many times. Why? Because we don't have the tapes and those that we do, can't be read by any equipment we have, not to mention undocumented skills, knowledge, experience and processes.