Sometimes it's valuable to look back at where and when you first learned something. My first contact with the ideas of David Allen were in the pages of Fast Company magazine. He took a lot of things in my life which didn't make sense and helped me sort them out.
Fast Company: Don't Manage Time, Manage Yourself (Interview with David Allen), 1998-Mar-31, by David Beardsley
We clutter our minds with vague promises about what we should do, what we could do. But there is always more to do than there is time to do it. Most of the stress that people feel doesn't come from having too much to do - it comes from not keeping agreements they've made with themselves. When you tell yourself you ought to do something and then don't do it, you experience self-doubt and frustration. You can fool all of the people some of the time, but you can't fool yourself for a second.