[dhdc]

> With any three things, you have harmony to humans.

In math, specifically dynamical systems, a lot of interesting stuff starts appearing after some variable goes up from 2 to 3, such as Period 3 Implies Chaos[1] for discrete maps, and the chaos in the 3 bodies problem. In continuous time systems, having 3 variable is the necessary condition for chaos to occur. My personal guess and take away is that having 3 of something is the bare minimum for nontrivial interactions to happen.

[1]https://sci-hub.se/https://doi.org/10.2307/2318254