Suppose you have 1000 actions listed, and that looking at the list as a whole, you perceive that it's a lot more than you're able to accomplish and you want to reduce the number.
The problem is that a human can only think of a limited number of things at once. When you look at one of the items on your list, you think of details of that item and you're not thinking about each and every one of the other items; so the one you're looking at seems more important than it ought to. The more intelligent you are, perhaps, the more you think of lots of details and implications of the item you're looking at. So it's hard to make a decision to delete it.
I think what's needed are methods that allow you to compare among a smaller number of actions. For example, comparing only two it may be relatively easy to decide "if I could only do one of these this year, which one would I want to do?"
-- Use the Horizons of Focus to divide stuff up like subdirectory trees with multiple levels. For example, when viewing at a higher level, you might decide "This Saturday I'll spend 3 hours on Area of Focus X". This decision is taken while comparing relative importance of various AOFs, not focussing on details of X. Later, at a lower horizon of focus, you decide how to divide up the 3 hours among various projects within the AOF.
-- Mark Forster's techniques "Do it Tomorrow", "Auto-Focus", "Day-Week-Month" or "Final Version". http://markforster.squarespace.com/
-- My Powers-of-Two system: Divide actions among folders each reviewed every 2**n days, so each day you review 2 folders. When reviewing, move things that seem less important or urgent into less-often-reviewed folders, and vice versa, or decide to move some elsewhere in your system, do them immediately or delete them.
Inability is an abstract thing involving comparison with alternate universes; it cannot be experienced.