I think that's mostly a format issue, the underlying message is solid.

> Everyone knows that multiple backups are important.

My experience and your experience are apparently not the same in this respect. And I look at a lot of companies every year. The number of times the question 'do you do trial restores of your back-ups' is answered with either 'what backups' or 'no' is way larger than what you'd expect.

And those are companies, not individuals where I'd expect the situation to be much worse.

> If I'd had multiple backups, and Dropbox had deleted items that I hadn't asked it to delete, I'd still be able to comment about that because data deletion is serious business.

Yes, absolutely it definitely is. Dropbox dropped the ball here. The problem is that you can pretty much expect them to drop the ball on occasion, no large service has every been 100% without data loss. Amazon, google, dropbox, microsoft, they've all lost some customer data at some point.

It's the rule, not the exception. When you're dealing with data data loss is the thing you're working hard to prevent but it'll never be 100% perfect. It can't be. There will always be edge cases and the simpler you try to make it on the outside the more complex the actual software becomes. Complexity leads to bugs, bugs (can) lead to data loss.

> This thread isn't (at least, shouldn't) be about data being deleted; it's about unpredictable behaviour from software.

All software that I'm aware of contains bugs. The discipline and experience required to write bug-free software is universally claimed to be present in one industry only: aerospace/aviation. And even there they have bugs, just fewer of them at massive expense. Bugs are the norm, not the exception.

> When that unpredictable behaviour includes deleting data that that's a valid serious concern even if everyone has great backup strategy.

Yes, it is a valid concern. And the way to mitigate that concern is by looking it in the eye and saying 'I don't trust software'. Any software. Including dropbox.