The general point of the sentence is fairly clear, meaning "a dream is just a dream". But what is the best way to think of the でしかない construction?
At first I saw it as 夢は夢で, as in, "a dream is a dream and...", but now I'm wondering how correct this is or if it's correct at all.
Is it better to look at it as a separation of the parts of である? Does this happen in many other cases, where you use a qualified で followed by ある?