The story beat where everything goes wrong at once and your protagonist's plan completely falls apart.
The all-is-lost moment is the structural beat, usually near the end of the second act, where the protagonist's plan fails catastrophically. The villain wins, the ally betrays them, the escape route closes, or the thing they were counting on disappears. It is not just a setback; it is the moment where the path the character has been on is destroyed and there is no obvious way forward. In Blake Snyder's Save the Cat framework, this beat often includes a 'whiff of death,' whether literal or metaphorical.
Without a genuine all-is-lost moment, your climax has no contrast. Stories need their lowest low to make the highest high feel earned. This beat also forces your protagonist to change strategy, dig deeper, or transform in some fundamental way, which is where the most compelling character development happens. If your character can just keep doing what they have been doing, you have not raised the stakes high enough.
Han is frozen in carbonite, Luke loses his hand and learns Vader is his father, and the Rebellion is scattered. Every single thread reaches its worst possible outcome simultaneously.
Nick discovers Amy's diary is fabricated and realizes the depth of her plan to frame him for murder, but he has no proof and the whole world believes he is guilty.
Amir finds Sohrab but learns the adoption is legally impossible, breaking his promise to the boy. Sohrab's suicide attempt makes everything feel irreversibly lost.
The all-is-lost moment should feel like the logical consequence of choices made throughout the story, not like the author randomly decided to punish the character. Set it up.
If the reader can immediately see how the character will recover, you have not gone far enough. The reader should genuinely wonder how the story can possibly end well.
The all-is-lost moment is the event. The dark night of the soul is the emotional reaction that follows. They are sequential beats, not the same thing.
Write a one-page outline of a story's second act. Include three escalating setbacks, each one worse than the last, that logically build toward an all-is-lost moment. Make sure the final catastrophe is a direct consequence of the protagonist's greatest strength becoming their greatest weakness. Then write the all-is-lost scene itself in 300 words.