GTD is like GPS for Time Management

I took off last week for family vacation, which we were fortunate to spend on the "outer Cape" of Cape Code. Thanks to my wife's suggestion, navigation this year was a snap because we finally got a GPS unit [1]. I expected the thing to be somewhat useful, but I was surprised - it absolutely blew me away. Just for fun I thought I'd play with the title's high concept pitch and share a few analogies to time management that came to mind.
Why did it have such a positive impact on me? It removed nearly all of the stress of navigating to somewhere new, leaving me free to simply drive. The analogy to work is that a productivity system like the one I teach (GTD is the closest thing) structures everything coming into your life, along with what you've decided to do, so that you can fully focus on your work. Both do this by making informed decisions prior to execution, i.e., by removing the unknowns, and simplifying and clarifying the process. In the GPS case, it knows navigation (where I'm going) and breaks the project (getting from here to there) down into tasks - drive straight, turn right, etc. I simply execute the plan it made with 100% of my attention. For productivity, when you process incoming stuff into tasks, you break bigger projects into small, executable steps that you can jump right into when you're ready for them.
Stepping up a level, I suppose the summation of all upcoming trips you've planned is the equivalent of your master projects list (multi-step objectives) - the many things that you've invited into your world that give direction to your life, based on your goals. The individual steps (turns, in GPS, and action steps, in GTD) are what actually get you there. I tell clients that you can't do a project, you can only do its individual actions. Can we look at a trip this way - you can't "do" a trip, you can only drive the segments? Hmm...
What's really worth the money is the trust I have in the thing. Before, navigation was extremely stressful for me due to the large number of unknowns, the difficulty of matching maps to reality, and the pressure of needing to get somewhere on time. I worked around these by adding analysis and time: Print maps, determine route based on advice from Google Maps (or better yet, someone whose been there), study the route, reverse-plan the arrival time based on estimate from the route, then start driving. To plan for the unplanned (anti-knowledge?) I had to allocate plenty of extra time
The lesson? No, it's not an ad for Garmin :-) It's more the value of having a trusted system, the relief it brings, and the empowerment of your attention. What do you think? Is there another analogy for a productivity system you want to share? I'd love to hear it!
References
- After a lot of research we bought a [1] Garmin nüvi 255W 4.3-Inch Widescreen Portable GPS Navigator. Recommended.