Underlying what we've been looking at is editing—that mystifying, disconcerting process of seeing your work darkly as in a mirror and seeing its defects, not as a writer sees them, which is usually as a parent sees an offspring, but as someone outside the work, a near stranger, the editor side of you, the side that's difficult to deal with but essential to develop to become a good, even great, writer.
Asking "why" is essential to the editing process. It's should be asked throughout the writing process, even when you fear the answers, not only because you don't want to know, but because getting at the answers takes effort—and time. But, in the end, it's better to ask yourself the tough questions and not leave this intimate business to others, because this is where writing gets personal, the heart of the matter, your heart, the most intimate part of a writer, the reason you write, or don't.
So, when you reach that part of the writing process that ties you in knots and makes you more than a little crazy, stop as you would at a washed out section of roadway. Ask yourself why the story or scene, dialogue or description isn't working. You can also ask the lesser questions—who, what, where, when and how—but none of these gets at the heart of the matter better than "why."
As a reminder, the three keys that unlock the power of why are to answer the question honestly, in detail and in writing. See the posts below for more information, and visit my online editing workshop, "Show and Tell: How to Know, How to Fix."