Never Say “Oops”
“Oops” is so frequently abused as error message copy that you would lose nothing by banning it entirely from your product.
“Oops! You need to log in first.”
I’m sorry, but where was the whoopsy? No one messed up. This is normal.
“Oops! That page doesn’t exist.”
The page was intentionally deleted. The user intentionally clicked a link that was once valid. Where’s the oops?
It’s much better to be factual. Apologize if you want to: “We’re sorry, you’ll have to log in first.” Or, “That page doesn’t exist or was deleted.”