This phrase is easier to
understand if it is read as "You can't eat your cake, and have it too".
Obviously once you've eaten your cake, you won't have it any more. Used for expressing the impossibility of having something both ways, if those
two ways conflict.
He works so hard to pay for that
fancy house of his that he never has any
time to stay home and enjoy it.
Yeah, you can't have your cake and eat it too.