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GTD is a "bottom up" approach that focuses on mastering the mundane. Once that is done, though, there are higher perspectives that can really make the system bring about great results.
The practice of setting aside dedicated time (typically a couple of hours) to make sure your system is clean, current and complete. David Allen regularly cites this as the critical success factor for GTD.
The perspective that focuses on your current commitments (projects).
The perspective that encompasses the areas of your life that you need to maintain.
The perspective that encompasses your 1 to 2 year goals.
The perspective that encompasses your 5 year vision.
The perspective that encompasses your whole life and why you're on the planet.
The perspective that focuses on the work that is right in front of you and already defined.
An approach to personal productivity that focuses on action management rather than time management. Based on the best-selling book of the same name.