An untested backup is a guess. Here is the twenty minute check that turns it into a fact.
Ask somebody whether they have backups and you will almost always get a yes. Ask when they last restored one and the room goes quiet.
That gap is where the damage happens. An untested backup is not a backup, it is a guess with good intentions behind it.
The failures are rarely dramatic. A sync folder that silently stopped syncing in February. A database dump that has been writing a zero byte file for months because a password changed. Backups running perfectly onto a drive sitting on the same desk as the computer, which is a fine answer to a dead hard drive and no answer at all to a burst pipe or a theft.
Ransomware made this sharper. Anything your machine can write to, ransomware can usually encrypt too, which includes the external drive you leave plugged in and the network share everyone has access to.
Here is the check. It takes about twenty minutes and you can do it today.
Pick one file that would genuinely hurt to lose. Restore it somewhere new, not over the original. Open it. Confirm it is the version you expected and not something from eight months ago. Then look at where that backup physically lives and ask what single event would take out both the original and the copy.
If the honest answer to that last question is a fire, a flood, or somebody walking off with the laptop bag, you have one copy in two places rather than two backups.
The rule worth keeping is old and still right. Three copies of anything you care about, on two different kinds of storage, one of them somewhere else entirely. For most people that is the working file, an external drive, and a cloud account. That is it. You do not need enterprise software to get there.
Then put a reminder in your calendar every three months to restore one random file. Not to check that the backup ran. To check that what came back out is readable.
Nobody enjoys this. It is the least interesting twenty minutes of your quarter. It is also the only version of this task that actually works, because the alternative is finding out during the week you can least afford it.