The key is multiple copies everywhere. Storage is cheap these days, so you can keep more than one copy - and digital hoarding doesn’t take up much space at all.
The problem with multiple copies everywhere that is:
1) You can never remember which copy is the master or the most recent. And a backup is not a backup unless you test the restore regularly. But with multiple copies, we don't have the time to test the restores of all the backups.
2) If any of the syncing scripts stop working, you will not know for ages. Unless you have another layer of monitoring scripts that watch your backup scripts. But almost no one has the patience to do that.
I have at least 3 copies of my important files, in 3 different locations. But I fail on both of my points above.
