Learning Lessons from Systems Thinking

I see this pattern over and over and over again. What can one do about it? One potential intervention point is to set a standard/policy on the "attention per project" so that when there is not enough time to do it properly, you do not accept it, thus maintaining quality work and therefore reputation (so in theory the project pipeline never dries up). GTD gives us more time to squeeze more in. Zero-in box helps us comfortably manage our email blizzard. Systems helps us identify problematic patterns and potential leverage points for change. Where can one go to learn "How to Say NO" ?