Developing the Dark Moment
Not all books need dark moments, but properly used, this point of crisis can intensify the conflict and at the same time, initiate its resolution.
Think of the dark moment as the time when the protagonist reaches rock bottom. All seems lost. This will usually precede the climax (where the major plot problem is resolved), and thus take place near the beginning of the final part of the book. This is when all the torturing you've done has its greatest effect. But, just as Mommy always tells Tot during the spanking, the torture is meant to build character. The protagonist should experience despair, and then through courage come out of it with redoubled determination and greater wisdom.
The 5 Ds of the Dark Moment:
Dilemma-- the situation has disintegrated around the protagonist, and all seems lost.
Desperation-- the protagonist flails about, considering the most extreme escapes from the dilemma.
Despair-- the protagonist surrenders to despair, certain that there is no way out.
Deconstruction-- in the calm that follows despair, the protagonist begins to analyze the situation, deconstructing needs, values, and options.
Decision-- the protagonist decides what can be discarded, and what's most essential to be kept, and determines a course to achieve that.
The climax is the working out of the decision the protagonist made as a result of the brutal deconstruction forced on him by the dark moment.
So the dark moment is something of an acid test, if you don't mind mixed metaphors. As novelist and writing teacher Jenny Crusie puts it, the dark moment can offer a moral dilemma, one that confronts the protagonist with a threat to the internal identity. It's a time to clarify what sort of "self" the protagonist wants to be. Somehow the darkness forces light on what seemed to be impenetrable conflict.