The thing is the Universe cannot distinguish between positive in negative but remember words have so much meaning especially when asking the universe for something. If you "want" something to happen you will always be wanting. If you "hate" something, you will always be hating it. Thats how words works. So it has been suggested that using words like hate, can't, won't, etc should be used in a limited capacity in terms of your goal. For example, if someone asked you to come to work early and you are unable you obviously are going to say you can't. That isn't going to slow down your manifestation.