pie in the sky; castles in the air; something unattainable
Idiomatic expression meaning something that looks good in theory but is impossible to realize, like a drawn rice cake that cannot be eaten. Often used to criticize unrealistic plans or dreams.
That plan is nothing more than pie in the sky.
If you only talk about ideals, it will end up as castles in the air.
Literally 'a rice cake drawn in a picture'. The phrase comes from the idea that a picture of a rice cake cannot be eaten, symbolizing something that is only good in appearance but useless in reality.