to build castles in the air ------ 异想天开

英文释义

To cherish extravagant hopes and unrealistic plans that will never succeed.

例句

My dreamy son needs to study for a serious profession and work hard if he wants to succeed, rather than just build castles in the air.

我的爱梦想的儿子必须去学习，从事一份正经职业，如果想成功，他得努力工作，而不能异想天开。