I made a not to serious attempt to implement GTD, but I got stuck on the granularity of "next action." I don't remember quite why this was, but as I was attempting to write my lists I would get stuck on something like this. (I'm a music producer). I need to mix a song on the next day. This tends to be a complex task that takes at least a few hours or many more. I would ponder: is the next action "go to the studio",or is it "turn on the computer", or is it "mix the song" or is it "organize the drum tracks." In my understanding (which was probably wrong) one idea of GTD was to break complex tasks down and represent them with a next step. I never found this helpful, as I always new what the next step was. What was hard was actually doing the work. It often takes longer than I want, and is sometimes hard to do when I'm not inspired. After a while I gave up, but I did get in the habit of keeping my email in box more organized.