Why can't I have my sentence?

After reading Heather Sellers passage on revision, one sentence stuck out to me: "A writer has to let go of favorite lines and passages in order to put all the focus on on the best part of the piece" (377). I disagree with this passage. I understand that if you have limited words to use and so much you have to say that there are certain parts that need to be disregarded. However, I am curious about why you cannot have wonderful lines and passages and use them to only enhance and improve another line or passage. Why can you not have two wonderful passages. Why must their only be one? I think that in order to improve your writing you should be able to write what you want and if one passage is stronger than another, take that as a challenge upon yourself to improve the other passages. Don't back down and take out the better passage, challenge yourself and improve what writing may be less than good. Everything should be used only to enhance your writing. The way Sellers offeres to handle the situation it sounds as if people should only back down and move on, and I think that is accepting defeat. Obviously sometimes there is nothing you can do to improve a piece, by why get rid of whats good? CHALLENGE YOURSELF!