Why is my backup not actually backing up?
Because backup systems fail silently far more often than they fail loudly — and the failure is usually discovered at the only moment it matters, when you try to restore. A backup you have never restored from is not a backup; it is an assumption.
The common silent failures:
It stopped running. A changed password, an expired token, a full destination, a disconnected drive, or an update that reset the schedule. Many tools report this only in a log nobody reads.
It is backing up the wrong things. Default selections frequently exclude exactly what you care about — external drives, network locations, application data, and anything outside the standard user folders.
Sync is not backup. This is the most consequential misunderstanding. A sync service propagates deletions and corruption — if a file is deleted, encrypted by ransomware, or overwritten with rubbish, that change syncs everywhere. Version history is what saves you, and it has a retention limit you should know.
One copy in one place. A backup on an external drive left permanently connected can be encrypted by ransomware or destroyed by the same fire, flood or theft.
The destination is full, and the tool has been failing for months.
Application data is not included — mail stores, databases and virtual machines frequently need their own backup method, because copying files while they are open produces an unusable copy.
Encryption keys not recorded. An encrypted backup you cannot decrypt is no backup at all.
What actually works:
The 3-2-1 rule: three copies, on two different media, with one kept off-site — the last of which is what protects against every local disaster.
At least one offline or immutable copy, which ransomware cannot reach.
Test restores on a schedule. Restore a handful of real files, and occasionally a full restore. This is the only verification that means anything.
Check notifications are actually arriving, and look at the log monthly.
Document what is covered and what is not, because the gaps are where the loss happens.