It is possible for a random error to affect two computers simultaneously, if they are made from the same assembly line, they may fail in exactly the same way, especially if they share the same wires.
That's the reason I sometime see that for RAID systems, it is recommended to avoid buying all same disks at the same time, because since they will be used in the same way in the same environment, there is a good chance for them to fail at the same time, defeating the point of a redundant system.
Also, to guard against bugs and design problems, critical software is sometimes developed twice or maybe more by separate teams using different methods. So you may have several combinations of software and hardware. You may also have redundant boards in the same box, and also redundant boxes
That's the reason I sometime see that for RAID systems, it is recommended to avoid buying all same disks at the same time, because since they will be used in the same way in the same environment, there is a good chance for them to fail at the same time, defeating the point of a redundant system.
Also, to guard against bugs and design problems, critical software is sometimes developed twice or maybe more by separate teams using different methods. So you may have several combinations of software and hardware. You may also have redundant boards in the same box, and also redundant boxes