How often do people use tired expressions about which they have little or no understanding? They seem like the appropriate thing at the time, but on numerous occasions we don’t put much thought into them.
I was almost a senior citizen before I grasped the meaning of “You can’t have your cake and eat it too.” Well why not? Though cake is the last thing I’d order at a restaurant (unless they’re out of pie), I understood the expression to mean you can’t have it and therefore can’t eat it. Why not? Too many calories? Too expensive? One ought to be able to have (own) the cake and then eat it.
Someone finally explained that it means you can own a beautifully decorated cake and admire it, show it off, bronze it, photograph it, but if you eat it, you can’t have it (any more).