What makes concurrency so hard?

The short version: Concurrency is difficult due to the state space explosion that occurs very quickly when you distribute a system, which exceeds our ability to model.

The author provides a neat demonstration of this hypothesis, and it really resonates with my own experience.

Recently, I’ve been thinking about this idea a lot since I discovered Residual Theory. In this theory, we begin with too many possible states to create an accurate model, but progressively reduce the complexity by focusing on attractors, solutions that cover large areas of the state space, so that unforeseen states already have a solution.