It is amazing what the brain can do after it has rested overnight.
Yesterday night, while I was working on my book. It reached a stage where I was not understanding what I was writing again. So I told myself that I should go to sleep because my brain needs rest.
So I went to bed and by this morning, when I woke up and went back to the book writing, things were more clearer to me and I was understanding what I was writing.
So the brain always needs it's due rest to rejuvenate itself.