There's a well-documented psychological effect where walking through a doorway causes you to forget what you were doing seconds before — the "doorway effect": you enter a room to get something and immediately blank on what it was, even though you remembered clearly one room over. Researchers who study this attribute it to how memory is organized around location: crossing a boundary, physically, seems to cue the mind to file away whatever belonged to the space just left.
It's a small effect, easy to laugh off. But it's also a strange piece of evidence for something anyone who has changed jobs, ended a relationship, or moved to a new city already knows without needing a study to prove it: crossing an actual threshold changes something in you that standing still on either side of it does not.
Anthropologists have a name for the space this happens in. Arnold van Gennep, writing in the early 1900s about rites of passage across cultures — coming of age, marriage, initiation — described most such rites as having three parts: separation from the old status, a liminal phase genuinely between statuses, and incorporation into the new one. Victor Turner picked up the middle phase decades later and gave it most of its modern texture: liminal people, he wrote, are "neither here nor there," stripped of the markers that would tell others — or themselves — what they are, for exactly as long as the passage takes.
What's notable is how consistently cultures have felt the need to mark that middle phase deliberately, rather than let people simply drift from one status to the next. A threshold, treated this way, isn't just the moment before the next stable state — it's a state in itself, with its own rules, its own discomfort, and a kind of clarity the stable states on either side don't have. You can see further from a threshold precisely because you're not yet committed to a direction.
This is different from anxiety about the future, though it's often mistaken for it. Anxiety asks what will happen. A threshold, actually attended to, only asks what is happening — right now, in the doorway, before the room on either side reclaims your attention.
Vesper Tesserae's corpus has a concept for exactly this middle position on nearly every axis it holds — a concept that doesn't lean toward either resolution, because the threshold itself doesn't lean.