When you know you'll get email to zero, you're free to deal with the ones you choose, when you choose. Most productive. - David Allen

I have found that lack of time is not the major issue for them (though they may think it is); the real problem is a lack of clarity and definition about what a project really is, and what associated next-action steps are required.

Pay appropriate attention to what has your attention, so you can pay attention to what really has your attention.

Getting things done requires two basic components: defining (1) what “done” means (outcome) and (2) what “doing” looks like (action). And these are far from self-evident for most people about most things that have their attention.