[pseudohadamard]

One thing you need to add is that UB can be incredibly subtle and almost impossible to spot even by people with decades of programming experience. However, the compiler - and we're talking almost exclusively gcc here - will spot it and silently break your code. It won't warn "hey, I've spotted UB here!" even with every possible warning enabled, it will just quietly break your code without giving you any indication that it's done so.

It's some of the most user-hostile behavior I've ever encountered in an application.