From the GTD Times:

Here is an interview with David Allen by the publisher of the Polish version of Getting Things Done.

Q: You developed the Getting Things Done Program because…
A: I had discovered that applying some rather simple techniques could have profound results, immediately, in people’s ability to focus, stay relaxed, and make positive progress in their work and lives

Q: What is the difference between GTD and normal task planning?
If you mean by “Normal task planning” that you make a list of things to do today, or this week, then the difference is that GTD recommends you keep track of every action that you might be able to take, plan as little as possible, and trust that you’ll make good intuitive decisions moment to moment from all your options. In other words, you need to remain flexible and open to all the new inputs and changes that are happening more and more frequently; and if you over-plan, it will get in your way.

Q: Order above all. That is the first rule of the GTD Program. What is the second one?
“Order above all” – not sure what that refers to (I never said it). There are not really any “rules” in GTD – only observations of principles. If you want to have a clear mind, you must capture externally whatever is keeping it from being clear, make executive decisions about what you’re committing to do about it, and park the results into some system that you can trust will reflect it back to you at the appropriate time.