This technique works on the theory that most chronic worry is just an endless feedback loop-your mind spins around and around about the same things over and over. Here you allow yourself to think about each problem, but not obsess about it. This allows you to focus on finding solutions, and not just spin. It also allows you peace of mind for the rest of the day-you've done your worry work and can now relax.
Ryan, M.J. Instant Health And Happiness. Pg. 205.