One that completely reframed how I view story generation was something an old professor mentioned in passing: start with a lie your character believes is true, and then make them prove it. Not just any lie, but something foundational to their identity. The most gripping friction in fiction rarely comes from external monsters, but from that moment the internal scaffolding collapses.
I’ve tried it with a character who believed he was a meticulous, controlled person. The prompt forced me to prove that lie by showing him meticulously planning a petty act of revenge against a neighbor over a hedge-trimming dispute. His 'control' was just obsessive rigidity masking total emotional chaos. The story wrote itself from there—it wasn’t about the revenge, but about the terrifying freedom he felt when his own lie was exposed and he had nothing left to prop himself up with.
These kinds of prompts work because they bypass the predictable 'what if' scenarios and go straight to character corrosion. Instead of 'what if there was a magic school?', it's 'what false truth does this student cling to to survive here, and what price do they pay when it unravels?' That's where the real spark is.