have your head in the clouds
US /hæv jʊər hɛd ɪn ðə klaʊdz/
UK /hæv jʊər hɛd ɪn ðə klaʊdz/

1.
心不在焉, 不切实际, 异想天开
to be impractical, unrealistic, or lost in daydreams
:
•
He always has his head in the clouds, dreaming of becoming a rock star instead of focusing on his studies.
他总是心不在焉,梦想着成为摇滚明星而不是专注于学业。
•
You need to stop having your head in the clouds and face reality.
你需要停止心不在焉,面对现实。