Full system recovery. That is, the computer system can not be used (it burnt in the fire, it got stolen, it got trashed beyond recover). You need to do a bare metal restore of the operating system onto different hardware before you can even consider getting your data back. The operating system has had numerous updates and modifications, as have the applications. Most of these have not been documented.
The database is always in use, and thus any backup is partially dated simply because it was changed between when you started the backup and when it completed. This tends to apply to online systems.
The system was originally configured for special purposes (perhaps speed of database access). You no longer have records of precisely what was done. The person who did it is no longer available.
Under there circumstances, could you quickly get a system working again?
RAID isn't a solution in itself. RAID supports single drive recovery, not loss of more than one.
Test your backup and recovery system. Most never get tested.
System image backup works reliably only if you have identical hardware to which to restore.