1 Mercutio: I guess Ophelia’s right. This time travel software is too dangerous. I should delete it.
2 Mercutio: And the copy on my laptop. And all the automated backups. And the GitHub repository...
3 {beat}
Mercutio: Or I can just forget about it. Bit rot should make it unusable in a couple of years at most.

Sometimes things are very difficult to delete.

Imagine you get a request from a client to delete their personal data from your systems. Okay, you can probably delete it from the live systems. Then there's the development staging copy. And the periodic backups, which may be off-site at a data centre. Which keeps its own backups of everything because nobody wants to use a data centre that can't guarantee restoration of your data even if something at the data centre fails. So they probably have backups in multiple physical locations.

And all these things are encrypted, because you don't want the data centre to read your client data. So to delete a single record from gigabytes of encrypted backup data... you'd need to decrypt the whole lot, delete that record, and re-encrypt it all. For each backup copy. And there isn't just one backup that's copied in multiple places. There are incremental backups and snapshots of your system every day for the past few years. All duplicated multiple times in your own company and your offsite backup data centre.

And then there may be physical backups on read-only media such as DVDs or whatever. That you can't erase without destroying the entire backup.

Just think about the periodic backup facility on your home computer (which you should have running if you value your data). Most such programs for home use don't even give you any ability to go back and modify a backup file. You can "delete" a file from your machine, but it's still there, in multiple old backups that let you restore it. There's no way to get rid of it except by deleting all your backups, which no sane person would want to do unless you're hiding evidence from prosecutors.

On the other hand, there are times when you can't find some file that you know you had somewhere, no matter what you try. Infuriating, isn't it?