This is something I try to get across to people on a daily basis. Raid is not a backup. Backup to at least 2 places to be on the safe side. Bad times for the hosting company
I echo the very excellent sentiments in these replies, along with the classic "a backup isn't a backup until you know you can restore from it."
Basically you shouldn't consider yourself to have a backup unless you have a backup of your backup. Also that you know that you can restore from it. More then once I've seen people say yes we have a backup, which they have but when they try a recovery it fails spectacularly!
I understand, but that still doesn't mean 2 backups = 1 backup. 2 Backups is 2 backups. Yes, one might fail on restore but so might both. In which case 2 backups equals no backup. I know that's silly, and less likely, but it's just an extension of what you said.
True. I think the saying stems more from not to relying on a single point of failure back up. It something I've seen mentioned and I like the ethos of it. If one of your backup solutions dies, there is a another to go off. Ideally best practice and due diligence would have these in separate buildings and have disaster recovery test in both, but I know it hard to do sometimes. My favourite is when people come in to test infrastructure redundancy by pulling random cables out of servers.
I always read this as: The first backup is the planned recovery process, the second backup is the backup plan in case the planned recovery fails. There is a certain redundancy to it though, unless you are using a different backup method for the second backup as well as it being stored in a different location.