I thought S3 was a worry-free storage option
Having recently emerged from an AWS exam, I thought that one of the selling points of S3 was that data is automatically replicated across multiple availability zones within a region without the customer needing to worry about the details. I also thought that the availability zones within a region were highly isolated from each other (e.g. separate data centres in different cities). I guess I'm wrong about at least one of those things.
At least the problem was largely fixed the same day. When problems occur within my employer's on-premises infrastructure, it usually takes several days to get it fixed, including a phase during which even the existence of the problem is denied.