Chocolate Cake

"You can't have your cake and eat it too."
What kind of stupid expression is that?
Why would you bother having some cake at all if you couldn't eat it?
Who makes this stuff up?
Don't get me wrong, I understand what the expression means, it's just that the cake analogy makes no sense. If you're a 10-year-old boy it means you can't sleep over your friend's house and expect your mom to clean your mouse cage while your gone. 

song: Chocolate Cake • artist: Crowded House