Are you backed up?

Back in the 70s, disk drives were about the size of washing machines. One type had two disk platters: one was embedded and could not be removed except by a technician, and the other was in a large plastic shell and was easily removable. Each platter held five megabytes. Yes, that's right: five whole megabytes, an insignificant amount of space now but humongous then.

Many used this dual platter drive to keep their operating system and database on the embedded one, and at the end of the day they'd copy it to the removable one. Then they would open the disk drive, take out the removable disk, store it in a safe, insert a new removable disk, and close the drive. Then they'd be ready for business the next day.

We got a call one morning from a customer. He couldn't boot. One of the techs went over to have a look and found that the embedded disk had a bad sector. It would need to be replaced.
Technician: "The embedded disk is bad. Are you backed up?"
Customer: "Yes!"

So the technician replaced the disk, snapped the old one in half so it would fit in the garbage can, and threw it away.
Technician: "I'm done -- she's all yours."
Customer: (after playing with the system a bit) "I can't find any of my data."
Technician: "Right -- you'll have to restore it."
Customer: "What does 'restore' mean?"
Technician: "Uh, it means you have to RESTORE it from a copy."
Customer: "Copy? What copy?"
Technician: "The one you make every night."
Customer: "WE DON'T HAVE A COPY!!!"
Technician: "When I asked you if you were backed up, you said YES!"
Customer: "We ARE backed up! We're SO backed up that we haven't had time to make any recovery disks!"