Everyone knows they should back up. Most people have something in place. Very few have ever checked that it works, which means most backups are a belief rather than a system.
Three decisions, not a slogan
“Three copies, two media, one off-site” is a good rule wearing a bad costume. Underneath it are three plain questions: how many copies exist, how many different ways could they all die at once, and is one of them somewhere else physically. The guide answers each for a normal household rather than a data centre.
Sync is not backup
The single most common failure. A synced folder mirrors your mistakes at the speed of light — deletions, corruptions and encryption included. There is a section on exactly where sync helps, where it does not, and how to tell which one your setup is doing.
The restore drill
Twenty minutes, once a quarter: pick a file, pretend the machine is gone, and get it back from each copy. This is the only test that distinguishes a backup from a folder you have been paying for. It also finds the boring failures — the drive that has quietly been unmounted since March, the cloud account whose payment card expired — while they are still boring.