Ask a business owner whether they back up their important data and the answer is almost always yes. Ask when they last restored from one of those backups to check that it works, and the answer is usually silence. That gap is the whole problem. A backup is not really a backup until it has been proven to bring your data back; until then it is a hopeful copy sitting somewhere, and hope is a poor plan for the day your main system fails. The uncomfortable truth is that a large share of backups quietly do not work when they are finally needed, and the only way to find out is to test them before the emergency rather than during it.
The ways a backup silently fails are numerous and unremarkable. The backup was set up once and stopped running months ago without anyone noticing. It has been copying the wrong folder, or missing the one database that actually matters. The files are there but corrupted, or encrypted with a password nobody wrote down, or in a format that requires software the business no longer has. The backup is on a drive sitting next to the computer it protects, so the same fire, theft or flood takes both. In every one of these cases the business felt protected, right up until the moment it discovered that the safety net had a hole in it that had been there all along.
A useful discipline for thinking about this is the simple rule of keeping several copies of anything important, on more than one kind of storage, with at least one copy kept somewhere physically separate from the original. The separation matters because the point of a backup is to survive whatever destroys the original, and a copy in the same room does not survive a fire in that room. The multiple copies matter because storage of every kind fails, and a single backup is a single point of failure wearing the costume of safety. None of this is complicated, but it only helps if it is actually running and actually complete, which brings the point back to testing.
The practical habit that turns backups from a comforting idea into real protection is to periodically restore from one and confirm you get your data back, intact and usable. This is dull, it is easy to postpone, and it is the single most valuable thing most businesses are not doing. A restore test tells you the backup is running, is capturing the right things, is not corrupted, and can be recovered by someone who knows how - the exact facts you desperately need to be true on the worst day, and the exact facts an untested backup leaves unknown. The business that tests its restores treats a failed hard drive as an afternoon's inconvenience. The business that merely has backups discovers, at the worst possible time, whether it truly did.