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I think it's the Snowflake Structure guy who plots out his books as "Three Disasters and an Ending." He likes a four-act structure rather than three (or five as on stage). So you have your initia...
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#4: Attribution notice removed
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/27061 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
I think it's the Snowflake Structure guy who plots out his books as "Three Disasters and an Ending." He likes a four-act structure rather than three (or five as on stage). So you have your initial Event which kicks off the plot. The protagonist decides to go on the adventure, whatever it is, and makes an initial foray. This fails. That's the end of Act One. Whatever that failure was sets up Act Two. The protagonist learns from this (or doesn't!) and more challenges ensue. But I think it's important that Act Two should be a direct result of the failure at the end of Act One. Lather, rinse, repeat for Act Two to Act Three. More challenges, the protagonist tries again, and fails _again_. There will be successes along the way, but the act will end in another Disaster. Now the stakes are much higher, because "people always stop after three." If you can't succeed on the third attempt, you'll never succeed, right? So the events from the first two acts are now boxing the protagonist in to make choices which lead to the Disaster at the end of Act Three. This is where I think your Black Moment comes in. The protagonist has tried three times to succeed, and each time those attempts have led to failure — possibly even building on one another. It's the choice of the Hero to move forward despite these failures which is the turning point, the big emotional impetus of the last Act of the story, which leads to the successful Ending.