Every post on HIY has room for exactly one comment. Not one per person — one, total, for the whole post. Whoever comes late sees what's already there and doesn't write over it. That's not a technical limitation we'll patch later — it's the entire point. But that's not how we started, and the road there was more uncomfortable than we thought.
The first version: 280 characters, unlimited
The very first prototype looked like every other social network: a post, a comment column underneath, as long as it wanted to be. 280 characters per comment, modeled on something everyone knows. We tested it internally for two weeks.
What happened is what anyone who's ever scrolled a comment section anywhere already knows: the first three comments were good. After that, what had already been said got repeated in different words. By comment twenty, nobody was scrolling that far anymore. The discussion technically existed; practically it only existed for whoever showed up first.
The intermediate step: 140 characters
Our first reaction was: make it shorter. Less room per comment forces precision, we thought. 140 characters, modeled on something else familiar. The result was, honestly, worse, not better — comments got shorter, but not sharper. People squeezed the same thought into fewer characters, and there were still fifty of them under every post. Brevity alone doesn't solve the problem of volume. We'd turned the wrong dial.
The actual mistake in the question
The turning point was a line in an internal test log: "Why do we even want fifty people to be able to comment under one post?" The honest answer was: out of habit. Because other networks do it that way. Not because we'd sat down and thought through what's actually good about it.
A long comment section is rarely a conversation. It's a pile of people trying to say the same thing in parallel without really replying to each other. The tenth comment usually hasn't read the first nine. What looks like a discussion is often just a stack of independent first drafts. We asked ourselves: what if you simply don't allow that stack to form?
One comment, 60 characters — why that number specifically
The solution we landed on: a post gets room for exactly one comment. The first person to write something that lands gets the spot — and after that, it's taken. No second comment displaces the first, there's only the one. Whoever wants to react has to make it count, because they know there's only this one shot, and it sits permanently next to the post, not in a list barely anyone scrolls to the end of.
60 characters isn't a sacred number — we tested between 40 and 90. Below 40 it got too clipped, every comment sounded like a keyword instead of a thought. Above 90, the old reflex crept back in: ramble, because there's room. 60 was the point where people in testing actually started thinking before typing — because every character counted, and because they knew there was no second chance once someone else had already claimed it.
What surprised us
We expected people to be frustrated when they arrived too late and the comment slot was already taken. It happened, but less often than expected — and when it did, it usually came as a new post of their own instead of a comment that wouldn't have made it in anyway. We hadn't planned that, but it fits: whoever really has something to say, says it independently, instead of squeezing into someone else's comment section where there wasn't room left anyway.
The side effect we like most: there's no race for the wittiest comment to win the most likes, because there's only one and it isn't rated. Short and meant it — that's enough.