We help the helpless (fanfic writer)

It depends on the story. The very short stuff, it's not meant to "go" anywhere. There's an idea and I lay it out, and it's meant to represent the situation as it is. Usually it's more character rumination than action. Ship fic ends when the couple gets together, unless it's a crack ship, in which case I may be satisfied with getting them in the same room and/or interacting positively. Hurt/comfort ends when the character has attained some sort of comfort, whether it's a solution to their problem or just some relief from it. Plotty stuff is complex, because I tend to go for action-light plots, which rules out, "we killed the thing!" as an ending indicator.