Oh, I think I just realised what people mean when they say ‘have your cake and eat it too’. 
They probably mean eating your cake and having your (uneaten) cake in your possession, both at once, which is impossible. 
To me it always sounded like you get a cake and then you eat it, which is much less impossible. I mean, if you have a cake, then you are most likely going to eat it, and if you are eating cake, then of course you need to have cake. You could give someone cake and not let them eat it, but why would you do that? Who does that?! Really, the phrasing is just needlessly confusing! :gutkato_kapturniĝas: