The motto is 'trust but verify', and indeed that goes for your backups as well. And incidentally that's one of the most failed items during the dd's I've done and after verification several companies turned out to have lived without backups at all.
It usually takes two things to go wrong for a disaster to happen: some $0.05 part that fails and a procedural error.
One of the first books that I read talked about the story of the backup tapes on the car seat that were erased when someone in Sweden (?) with heated seats drove home. (urban legend iirc).
Iirc Saab pioneered heated seats because one of their engineers had colon cancer and Saabs are pretty common in Sweden, but I'd still wager that's an urban legend because the heating is done with DC current and to reliably alter the contents of a tape you'd need a lot more of magnetic field to overcome the resistance of the magnetic particles to change direction (remanence) and you'd want that field to alternate.
It usually takes two things to go wrong for a disaster to happen: some $0.05 part that fails and a procedural error.
And the consequences can be just about anything.