I use quotations marks there, because they are basically "Hey, what if ___?" and then no idea how a plot would work out.
And then I have one idea that I liked, except the idea is a premise, not a plot, and IDK how to do 20k of it without the fic being just Sam at Stanford, and the premise slotted in there, weirdly. (In which case it then becomes a Stanford fic, and looks a lot like an immediately prequel to Postcards).
Seriously. Like, the only possible "idea" I have that has a pre-determined beginning, middle, and end is the Big Bang I was gonna do a few years ago that is 18k with the worst pacing fucking EVER. The fic is supposed to span a few months and then at 18k I realized that ABOUT A WEEK HAD PASSED IN FIC-TIME.
If anyone happens to have ideas for 20k+ fics, especially ones that are SPN or J2, I would welcome them in the comments. This is a hint.