Don't ruminate on what can't be done – focus on what you can do. You never want to get stuck in the ruminating stage, because it prevents you from taking the action you need to move on. When you ruminate, start writing down your daydreams. The writing will transport you from the mental stage of the dreamer into the privileged world of the observer of yourself. Your writing will induce your daydreams to flow out of your mind. The disagreeables will evaporate. You'll stop chewing the cud. You'll realize that there are many more chances for you to be successful than you assumed.