Why your protagonist's longing should lead to their fear
What your protagonist longs for is what they'd have if their deepest fear didn't run them, so chasing it should walk them into that fear, or the longing is decoration.
The selfish version of the goal your protagonist gives up
Nearly every goal carries a selfish version, how your protagonist would get it if nobody else counted, and that version is what the turn asks them to give up.
Almost every goal has a selfish version. That's the one your protagonist has to give up.
Take what your protagonist consciously wants, what StoryDNA calls The Want. Not every want is selfish. Plenty of protagonists want to save someone.
But ask how your protagonist would get it if nobody else's feelings or safety counted. That's the selfish version. The Lie, the false belief your protagonist lives by, quietly approves of it, because it's the shortcut.
In Toy Story, Woody's selfish version is getting rid of Buzz and staying the only favorite.
Naming it does two jobs. It shows you exactly what your protagonist will have to give up when your story turns, so the sacrifice is specific instead of vaguely noble.
And it tells you what your story's temptations should look like. Every chance to take the shortcut is a chance to show which way your protagonist will go.
Almost everyone carries a wish they'd make if love and consequences didn't exist. Growing up means giving that one up.
So write one line: how your protagonist would get what they want if nobody else counted. Then build a scene where that shortcut is right there, and they have to choose.
How a character's need surfaces over the story
What your protagonist needs moves from something they'd deny, to flickers they push back down, to something undeniable once their false belief breaks, and that movement is the arc.
When your protagonist wins without changing
If your protagonist wins the goal without changing and the story treats it as a triumph, the story has adopted their false belief.