I learned this the hard way by getting too casual with Angelfire keeping an old website running for 20 years after I stopped updating it.

It had lots of photos that I hand-scanned from printed film, back in the day when it took a good bit of time to scan photos manually.

The site was a running joke, where I would open it to show people that it still existed... until it didn't, and I couldn't find my backup of all of the photos. The archive sites have the 'bones' of the website, but not the photos. It was easily avoidable, which is why it is painful.