Why ten seats

A bench has ten seats. It's an environment variable, so it can be changed in a second, and yet it hasn't moved since day one.

Below that, the bench is fragile. With three people, if two go quiet, the third is alone in a lit room. Silence becomes awkward instead of comfortable.

The ceiling

Above fifteen, something else breaks. You stop tracking who is who. The names lose their power — Firmin isn't a person any more, he's a label in a list. Messages overlap, replies arrive out of sync, and you get a feed, which is precisely what we were trying not to build.

Ten is roughly the number of people you can hold in your head without effort. It also happens to be how many fit on a long bench, if you squeeze up a bit and accept touching elbows.

When a bench is full we don't extend it: we create another one. A full bench is still a bench; an elastic bench becomes a room.