Backup tapes...
Back yonkers one of our clients did his usual backup, and locked the tapes up in his fireproof safe (onsite). This was in the heady days of Novell 3.12...
Came back the next day, PC's was gone. Server was gone. Safe (with tapes inside) was gone. No hard copies.
Oops.
And the taxman was busy with an audit on him...