They are very inspiring.
My own method (even before I used GTD) is to give estimated duration to every task. This has a double effect: 1. it shows whether it's actionable or not (enough time available?) and 2. it gives a motivation kick - I'll try to get it done in less time, just like in a competition game with yourself.
When I began to adopt GTD, I feared to give up this manner. But then I detected that both ways don't exclude but complement each other. Since then I benefit from both