As most who read my blog on a regular basis, I am a fan (and consultant) of Theory of Constraints. On a personal level, I really like how the TOC concepts blend with a lot of the personal effectiveness concepts. A big element of both is stop doing so much. More specifically, get rid of all the work in process, and focus on getting things done.
On the other hand, I was reading a semi-random interview with Jason Womack at the Lijit blog. He mentioned his coaching philosophy of "just get started." An I see a lot of benefit to this view too. As they say, if you never try, you will never succeed.
So which is it? Do it now? Do it later?.
From my perspective it is both. The idea behind "Just Do It" is to stop thinking about it, pondering, wavering, and just jump right in. The idea behind "clear out the files" provides focus and the opportunity to see what it is that should be Just Done.
My take on why people get stuck is that they have too much sitting in front of them to potentially do, and they have a hard time deciding which one to do -- or what to do about it when they look at it. So, pick up the next thing and see if there something that could be done there.
It's both: Cut out the excess crud, decide on a next action, and take the action.