Why things crawl back into your mind | GTD Times
You didn’t clarify enough. If your mind thinks there is more planning or brainstorming to do about that, or what you captured as a next action is not the next physical, visible step, it will take it back.
You’re not reviewing enough. If your mind doesn’t trust you’re looking at that choice often enough (Are we doing anything about this??), it will take the job back. The Weekly Review is gold. It’s not just clean-up time, it’s reassurance time for your mind that you’re “on it,” even if that’s a decision to let it incubate some more on Someday.
Good Stuff from David Allen's GTD Team. I can certainly say that this has applied in my use of GTD ... typical mistakes are not clarifying enough and not reviewing enough. I'm not too shabby on the review aspect, but sometimes do not take the time to really clarify what I need to do.