There's a post on Next Action Associates titled "Are you playing the game blindfolded? Check, mate. " which spoke to me. Part of my difficulty with next actions is thinking that I'll be smart enough to unpack something like "Check online for the thing" when I'm days away from the incident that sparked it. Sure, eventually I can figure it out, but most of the time I have to exert some mental effort to put myself back into the mindset that generated the next action. That's a lot of work, and can lead to my biggest bugaboo - procrastination.
I'm using the metaphor of multiple chessboards to help myself understand that I'm not just playing one game (my work) and instead am playing multiple games (my next actions and projects) to better help myself create a way for me to win each of those little games.
I've been doing GTD in some form since 2001 and it's interesting to me that I'm still learning more and more as I progress.