That’s why nobody uses it correctly. When someone wants the impossible or undoable...the response is: So you want to eat your cake and have it too? The way most people use it is in fact possible and doable. You want to have your cake and eat it too. In fact you can have your cake and then eat it. The real trick is to eat your cake and still have it...can’t be done...It’s just a minor peeve of mine.
I've never really thought about it, but you are right.