Data that isn't backed up (as in a second copy) doesn't really exist.
Likewise: data that isn't backed up off site isn't really backed up.
Likewise: data that isn't backed up off site isn't really backed up.
An IMO more realistic statement: Data that is not backed up is implicitly classified as "nice to have" - in many cases a perfectly rational choice, if done consciously.
> Likewise: data that isn't backed up off site isn't really backed up.
You may as well argue that no data is ever "really" backed up because there is always the possibility of simultaneous failure. It's always a choice of how much risk you're willing to accept vs. how much money and effort it would cost to reduce it further.
This proves by induction that no matter how many backups you have, it's not enough.
There are several horror stories of people going to their offsite tape backups to restore some lost data only to find that their backups didn't work due to a malfunctioning tape drive.
Other stories about encrypted backups where the decryption key is lost (backup data is encrypted with a randomly chosen "session" key, session key is encrypted using a public key, no-one could find the appropriate private key to decrypt the session key.
etc...
In the event of the failure that revealed the problem, they lost about 7 months worth of data (which was the time since the computer had last been connected to the network, and had synced via Active Directory, or whatever they call it.)