There are some here that are okay, but a lot just shouldn't be said (like "I told you so").
If I told someone something and they ignore it, potentially even multiple times why should I not say it?
Maybe you're fine with the likely outcome. But maybe not.
* And there’s a distinction between what’s likely to happen and what you think should happen. They’re not always the same thing.
If you make a prediction correctly, and it is ignored, then that's an indication that you should either make it more assertively next time, or you just can't work with this person.
And anyway, some humbleness is due -- sometimes we think we've given good advice, but it ends up being somehow inapplicable to the problem for reasons that are outside our scope.
- Remind them next time it's relevant - "Remember last time we touched this service and the Widget crashed and took the rest of switch down with it? I think this could be similar and we should reconsider my plan to isolate the network before hand."
- Mention it to your manager. Failing to heed a warning can be blameless and rational, but if you're consistently right when others aren't that's a sign you should have more formal influence (and responsibility). You won't get that by complaining to peers.
- If it was extremely serious (it rarely is - the really bad stuff is usually stuff no one foresaw) and your concerns dismissed out-of-hand (also rarely the case - people legitimately have different priorities), discuss it with your/their manager.
You can also of course do it if there is no other escalation path - CEOs and EMs ideally didn't get where they are by being unable to take criticism - but you should also be very sure your advice really was right, and not a stopped clock.