3 is the first number with a third party watching. 1 is the self, 2 is a private matter between two, and 3 has an audience — which is where expression, story, and telling it to people who aren't in the room all begin. That explains 3's central trait: you don't think it through and then say it, you say it and then it's thought through. Language isn't your output; it's part of the thinking.
You'll recognise it here: an idea that sat still for three days takes shape in twenty minutes of talking; halfway through explaining something you discover what you actually think; and too long alone dulls you — not from wanting company, but from lacking a wall to throw ideas at and have them come back.
Running well, 3 makes things travel: the same subject, passed through you, becomes something people want to hear and manage to remember. That's scarce in any field. Blocked, it goes two ways. One is scatter: the ideas outrun the doing, so you tend to be carrying ten excellent beginnings. The other is using liveliness to cover a hollow — the more you say, the further you get from yourself. 3's work isn't saying less. It's picking one thing and saying it all the way down: say the same idea a hundred times and you'll find it has become a body of work rather than talk.
