head in the clouds

“Head in the clouds”脑袋在云里，可以用来形容想法飘飘然，不切实际，所以正确意思是“胡思乱想，思想开小差”，其反义词就是：have one's feet on the ground; be down-to-earth(脚踏实地)。

Jack always has his head in the clouds. That's why he is still there.

杰克总是不切实际。这就是他一直停滞不前的原因。

Rather than having his head in the clouds, he needs to be more pragmatic.

他还是不要再白日做梦了，应该更加实际一点。