This is not Unix specific, but the concept is just the same regardless of OS.
Back in my xBase days I was working for a medical software company here in Dallas. I wrote an upgrade install batch file that would pkzip the FoxPro programs, database and back it all up and then delete all the files, re-install the upgrade and then unzip the database, recreate indexes, etc.
I tested the routine time after time and the world was a happy place until I got "The Call".
It seems that while the client had pkzip install on their machine, it wasn't in the path. The backup zip was never created, but the sub-dirs were blown away just the same.
Data was gone. No more, non-existant, poof.
Disaster recovery? Client never even heard of a backup.
The only way that I kept my job was that I spent the entire weekend on the client site manually re-entering data via our application and getting things up and running.
Luckilly for me, it was a slow site and I was able to do all the data entry in a single weekend.
Very, very painful lesson learned. When doing any thing destructive, check, double check, triple check and trust NOTHING.