to have one's head in the clouds ———— 不切实际（成语）

英文释义
(IDIOM) To be impractical; to be dreaming instead of facing matters at hand.

例句
Our company's elderly founder has a son who will someday be our boss, but we worry because he always has his head in the clouds, and can't be trusted to manage our company well.
我们公司的年迈创始人有一个儿子，他有一天将会成为我们的老板，但是我们担心，他不切实际，无法很好地承担管理公司的工作。