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。