I am always amazed by how realistic dreams can be. I have this thought that the brain simply could make us believe that they are realistic. I mean something similar when the ,giraffe-elephant hybrid in the tuxedo reading book, in dreams seems normal. Wouldn't it be possible for the brain to just fool us about the realism of our dreams?

On the other hand, the brain generates everything that we perceive in real life what prevents it from achieving the same level of realism in dreams?