So, what Hari does is basically game theory on a massive scale. The larger the group, the less complexity because you’re abstracting the different possible issues individuals would have out of the problem. Instead of making it more complex, it simplifies the whole thing because all the chaotic bits cancel each other out.
And slight spoiler warning for an old story but you find out later that the whole thing isn’t just predicted ahead of time and let loose but a group of people follow along in the shadows to keep the plan on track.