castles in the air
A rich man asked an architect to build a three-story house for him.
When the first story was finished, the rich man said to the architect: "I want only the third story; not the first and second stories."
The architect asked, "But without the first and second stories, how can I build the third story?"
Shaking his head, he packed up his things, and left.
英文中“空中楼阁”可以说成“castles in the air”，基本就是直译了，所以不难理解哦~
英文解释是“plans or hopes that have very little chance of happening”，也就是指“发生机会微乎其微的计划或者希望”。
She tells me she's planned out her whole career, but as far as I can see it's all just castles in the air.
Before you start building castles in the air, just think how much all this is likely to cost.