I think it was David Allen who said you can do anything you want, but you cant do everything you want. Its ironic how an attempt to do everything will actually keep you from doing anything. --Shawn Blanc
A few weeks ago, I tweeted that I had reached "OmniFocus Zero". I pulled up my available tasks one morning only to find that I had nothing to do. That's not to say that there were no more tasks waiting for me in OmniFocus, it's just that my Available perspective was empty. I had nothing due that day and no tasks that weren't blocked or waiting on someone else.
A few of my GTD-doing friends expressed disbelief. How could everything be done? The simple answer is that I'm ruthless. I'm ruthless when it comes to delegating, deleting, and deferring until later.
I do my weekly review every Monday morning. One of my favorite things is when I come across a task that is no longer relevant to my life. That means I can delete it. Not only from my task manager, but, more importantly, from my brain. It's one less open loop flying around my mind.
But it wasn't always like this. I used to be a task hoarder. I'd write down absolutely everything, and never get rid of anything. I'd just keep kicking the can down the road foolishly and naively thinking I'd get to all of those tasks someday.
The trick I finally learned was to give yourself permission to forget. You have to make a ruthless decision and give yourself permission to admit that you're never going to get around to that task and just delete it. If you have an item on your task list that is causing you anxiety because you just can't get around to doing it - then maybe it's not really something you're committed to doing at all. Get rid of it.
You have to come to the realization that you can't do everything. Sometimes, one concrete action is all you need to keep moving forward.