Well I like that in the movie "The Secret" they say that an affirmative thought is a few times more powerful than a negative thought. That's extremely soothing mentally because you don't have to worry everything in everyday life and that includes the thoughts you have.
What it does mean is that you can be aware of what you're thinking and as soon as you get a negative thought you can make an immediate switch to positivity. For example, if you have a negative thought about a person you can think about something you like about the person or a fond memory of said person. Obviously you have to make this work for you but I find it keeps me in a positive frame of mind.
Have a nice day.