castles in the air

US /ˈkæsəlz ɪn ðə ɛr/
UK /ˈkæsəlz ɪn ðə ɛr/
"castles in the air" picture
1.

空中樓閣, 不切實際的幻想

plans or hopes that are unlikely to come true

:
He's always building castles in the air about becoming a millionaire.
他總是對成為百萬富翁抱有空中樓閣般的幻想。
Don't waste your time on castles in the air; focus on achievable goals.
不要把時間浪費在空中樓閣上;專注於可實現的目標。