dreams or plans that are impossible or unrealistic
不可能または非現実的な夢や計画 (fukanou mata wa hi genjitsuteki na yume ya keikaku)
"He’s always building castles in the air about his future."
"彼はいつも自分の未来についてキャッスルズ イン ザ エアを作り続けています。" (kare wa itsumo jibun no mirai ni tsuite **castles in the air** wo tsukuri tsuzuketeimasu)
to create your own way of achieving success or independence
the time for something or someone has ended
to fail completely or embarrass oneself
As I understand; based on what I know
to hear a rumor or unofficial news
to act according to the advice you give to others
