Translation guide
An unrealistic hope or promise of future happiness or success that is unlikely to happen.
Expressing that a plan, idea, or promise is too idealistic and unlikely to be realized.
Literally 'an empty theory on a desk' — an idea that works only in theory, not in reality. Often used for academic or business proposals that are unrealistic.
His proposal is nothing but pie in the sky.
Literally 'a dream story' — a fanciful, unrealistic tale or idea. Conveys that something is too good to be true.
Winning 100 million yen in the lottery is just pie in the sky.
Literally 'a tower on sand' — something built on an unstable foundation, doomed to fail. More literary and less common in daily speech.
That promise was pie in the sky.