Today I had one of those flashes where something suddenly dawns on you. I realised something which is in some ways common sense and should be blindingly obvious, but which I think bears spelling out explicitly as we tend to forget it...
In discussing GTD, we often talk about the "trusted system". If we can't trust our system, we can't get to the "mind like water" stage. But what I realised is that you'll never be able to trust your system if you can't trust yourself first. For example, if I can't trust myself to systematically whip out my Palm or notepad or whatever each time something comes up that I have to remember or that I have to act upon, then "mind like water" remains an illusion.
Stated differently, you might say that you are part of your system yourself. And in order to trust this important part, you have to develop the necessary habits, i.e. to acquire some automatic behaviours. Without this, everything else you may try is largely irrelevant.