This is the low point for the hero or heroine. Of course you can have black moments for more than one character in a story. There are certain steps to follow in building this time in a character's life.
The first step is belief. The character who is going to face this must believe they are about to lose everything. If the reader isn't convinced this is true, the moment will fall flat and no one wants this to happen in their story.
The writer needs to build toward this moment. Throwing it in at the last moment makes it seem contrived. Once the blocks are in place the moment arrives. The character suffers and squirms until the resolution time arrives. This resolution can be happy or unhappy depending on the kind of story the writer is telling.
Though there can be black moments for more than one character in the story, there are some points to remember when developing this part of the story and some pitfalls to avoid.
The wrong focus character.
The wrong timing.
Use of outside forces to precipitate the moment. The black moment should be centered on the character's inner conflicts.
Inner conflicts too easily solved.
The use of coincidence or misunderstandings.
So when planning for this part of the story, choose carefully and think this through carefully.