"Oops! An unexpected error has occurred."
1. Isn't 'unexpected' implicit in the need to notify the end user of an unspecific error they have no agency to attend to? "Sorry, breaking character here and pulling back the curtain, Something Didn't Go As Planned. Whoops."
2. After the first three screenfulls of such alerts, the error is no longer exactly unexpected by said user, contextually speaking.
3. I need more sleep and/or coffee.
@Momentrabbit I find that most developers write code that assume that everything will have been going to plan up until that point at every point, which means that once one thing has gone wrong, the likelihood of more things going wrong goes up sharply.
Most users intuit this quickly. Most software, sadly, does not.